Temperature compensating bulk acoustic wave (baw) resonator structures, devices and systems

ABSTRACT

Techniques for improving Bulk Acoustic Wave (BAW) resonator structures are disclosed, including filters, oscillators and systems that may include such devices. A first layer of piezoelectric material having a piezoelectrically excitable resonance mode may be provided. The first layer of piezoelectric material may have a thickness so that the bulk acoustic wave resonator has a resonant frequency. The first layer of piezoelectric material may include a first pair of sublayers of piezoelectric material, and a first layer of temperature compensating material. A substrate may be provided.

PRIORITY CLAIM

This application is a continuation of PCT Application No.PCT/US2020043752 filed Jul. 27, 2020, titled “TEMPERATURE COMPENSATINGBULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES AND SYSTEMS”,which claims priority to the following provisional patent applications:

-   U.S. Provisional Patent Application Ser. No. 62/881,061, entitled    “BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES AND SYSTEMS”    and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,074, entitled    “ACOUSTIC DEVICE STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul.    31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,077, entitled    “DOPED BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES AND    SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,085, entitled    “BULK ACOUSTIC WAVE (BAW) RESONATOR WITH PATTERNED LAYER STRUCTURES,    DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,087, entitled    “BULK ACOUSTIC WAVE (BAW) REFLECTOR AND RESONATOR STRUCTURES,    DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,091, entitled    “MASS LOADED BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES    AND SYSTEMS” and filed on Jul. 31, 2019; and-   U.S. Provisional Patent Application Ser. No. 62/881,094, entitled    “TEMPERATURE COMPENSATING BULK ACOUSTIC WAVE (BAW) RESONATOR    STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul. 31, 2019.

This patent is also a continuation of U.S. patent application Ser. No.17/380,011 filed Jul. 20, 2021, entitled “STRUCTURES, ACOUSTIC WAVERESONATORS, DEVICES AND SYSTEMS TO SENSE A TARGET VARIABLE”, which inturn is a continuation of U.S. patent application Ser. No. 16/940,172filed Jul. 27, 2020 (issued as U.S. Pat. No. 11,101,783 on Aug. 24,2021), entitled “STRUCTURES, ACOUSTIC WAVE RESONATORS, DEVICES ANDSYSTEMS TO SENSE A TARGET VARIABLE, INCLUDING AS A NON-LIMITING EXAMPLECORONAVIRUSES”, which in turn claims priority to the U.S. ProvisionalPatent Applications:

-   U.S. Provisional Patent Application Ser. No. 62/881,061, entitled    “BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES AND SYSTEMS”    and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,074, entitled    “ACOUSTIC DEVICE STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul.    31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,077, entitled    “DOPED BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES AND    SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,085, entitled    “BULK ACOUSTIC WAVE (BAW) RESONATOR WITH PATTERNED LAYER STRUCTURES,    DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,087, entitled    “BULK ACOUSTIC WAVE (BAW) REFLECTOR AND RESONATOR STRUCTURES,    DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,091, entitled    “MASS LOADED BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES    AND SYSTEMS” and filed on Jul. 31, 2019; and-   U.S. Provisional Patent Application Ser. No. 62/881,094, entitled    “TEMPERATURE COMPENSATING BULK ACOUSTIC WAVE (BAW) RESONATOR    STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul. 31, 2019.

Each of the applications identified above are hereby incorporated byreference in their entirety.

TECHNICAL FIELD

The present disclosure relates to acoustic resonators and to devices andto systems comprising acoustic resonators.

BACKGROUND

Bulk Acoustic Wave (BAW) resonators have enjoyed commercial success infilter applications. For example, 4G cellular phones that operate onfourth generation broadband cellular networks typically include a largenumber of BAW filters for various different frequency bands of the 4Gnetwork. In addition to BAW resonators and filters, also included in 4Gphones are filters using Surface Acoustic Wave (SAW) resonators,typically for lower frequency band filters. SAW based resonators andfilters are generally easier to fabricate than BAW based filters andresonators. However, performance of SAW based resonators and filters maydecline if attempts are made to use them for higher 4G frequency bands.Accordingly, even though BAW based filters and resonators are relativelymore difficult to fabricate than SAW based filters and resonators, theymay be included in 4G cellular phones to provide better performance inhigher 4G frequency bands what is provided by SAW based filters andresonators.

5G cellular phones may operate on newer, fifth generation broadbandcellular networks. 5G frequencies include some frequencies that are muchhigher frequency than 4G frequencies. Such relatively higher 5Gfrequencies may transport data at relatively faster speeds than what maybe provided over relatively lower 4G frequencies. However, previouslyknown SAW and BAW based resonators and filters have encounteredperformance problems when attempts were made to use them at relativelyhigher 5G frequencies. Many learned engineering scholars have studiedthese problems, but have not found solutions. For example, performanceproblems cited for previously known SAW and BAW based resonators andfilters include scaling issues and significant increases in acousticlosses at high frequencies. Further, the foregoing may exhibitundesirable drift in frequency characteristics over a range of operatingtemperatures.

From the above, it is seen that techniques for improving Bulk AcousticWave (BAW) resonator structures are highly desirable, for example foroperation over frequencies higher than 4G frequencies, in particular forfilters, oscillators and systems that may include such devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram that illustrates an example temperaturecompensating bulk acoustic wave resonator structure.

FIG. 1B is a simplified view of FIG. 1A that illustrates acoustic stressprofile during electrical operation of the temperature compensating bulkacoustic wave resonator structure shown in FIG. 1A.

FIG. 1C shows a simplified top plan view of a bulk acoustic waveresonator structure corresponding to the cross sectional view of FIG.1A, and also shows another simplified top plan view of an alternativebulk acoustic wave resonator structure.

FIG. 1D is a perspective view of an illustrative model of a crystalstructure of MN in piezoelectric material of layers in FIG. 1A havingreverse axis orientation of negative polarization.

FIG. 1E is a perspective view of an illustrative model of a crystalstructure of MN in piezoelectric material of layers in FIG. 1A havingnormal axis orientation of positive polarization.

FIGS. 2A and 2B show a further simplified view of a temperaturecompensating bulk acoustic wave resonator similar to the temperaturecompensating bulk acoustic wave resonator structure shown in FIG. 1Aalong with its corresponding impedance versus frequency response duringits electrical operation, as well as alternative temperaturecompensating bulk acoustic wave resonator structures with differingnumbers of alternating axis piezoelectric layers, and their respectivecorresponding impedance versus frequency response during electricaloperation, as predicted by simulation.

FIG. 2C shows additional alternative temperature compensating bulkacoustic wave resonator structures with additional numbers ofalternating axis piezoelectric layers.

FIG. 2D shows a temperature compensating bulk acoustic wave resonatorstructure similar to one shown in FIG. 2B, but in more detailed view

FIG. 2E shows another additional alternative temperature compensatingbulk acoustic wave resonator structures.

FIG. 2F shows a comparison of two example bulk acoustic wave resonatorstructures, one including an alternating axis arrangement of halfwavelength thickness temperature compensating piezoelectric layers, andthe other including an alternating axis arrangement of half wavelengththickness piezoelectric layers that are not temperature compensating,along with two comparison diagrams.

FIGS. 3A through 3E illustrate example integrated circuit structuresused to form the example temperature compensating bulk acoustic waveresonator structure of FIG. 1A. Note that although AlN is used as anexample piezoelectric layer material, the present disclosure is notintended to be so limited. For example, in some embodiments, thepiezoelectric layer material may include other group IIImaterial-nitride (III-N) compounds (e.g., any combination of one or moreof gallium, indium, and aluminum with nitrogen), and further, any of theforegoing may include doping, for example, of Scandium and/orMagnesium-based doping.

FIGS. 4A through 4G show alternative example temperature compensatingbulk acoustic wave resonators to the example bulk acoustic waveresonator structures shown in FIG. 1A.

FIG. 5 shows a schematic of an example ladder filter using three seriesresonators of the temperature compensating bulk acoustic wave resonatorstructure of FIG. 1A, and two temperature compensating mass loaded shuntresonators of the temperature compensating bulk acoustic wave resonatorstructure of FIG. 1A, along with a simplified view of the threetemperature compensating series resonators.

FIG. 6 shows a schematic of an example ladder filter using fivetemperature compensating series resonators of the temperaturecompensating bulk acoustic wave resonator structure of FIG. 1A, and fourtemperature compensating mass loaded shunt resonators of the temperaturecompensating bulk acoustic wave resonator structure of FIG. 1A, alongwith a simplified top view of the nine temperature compensatingresonators interconnected in the example ladder filter, and lateraldimensions of the example ladder filter.

FIG. 7 shows an schematic of example inductors modifying an examplelattice filter using a first pair of temperature compensating seriesresonators of the temperature compensating bulk acoustic wave resonatorstructure of FIG. 1A, a second pair of temperature compensating seriesresonators of the temperature compensating bulk acoustic wave resonatorstructure of FIG. 1A and two pairs of cross coupled temperaturecompensating mass loaded shunt resonators of the temperaturecompensating bulk acoustic wave resonator structure of FIG. 1A.

FIG. 8A shows an example oscillator using the temperature compensatingbulk acoustic wave resonator structure of FIG. 1A.

FIG. 8B shows a schematic of and example circuit implementation of theoscillator shown in FIG. 8A.

FIGS. 9A and 9B are simplified diagrams of a frequency spectrumillustrating application frequencies and application frequency bands ofthe example temperature compensating bulk acoustic wave resonators shownin FIG. 1A and FIGS. 4A through 4G, and the example filters shown inFIGS. 5 through 7, and the example oscillators shown in FIGS. 8A and 8B.

FIG. 10 illustrates a computing system implemented with integratedcircuit structures or devices formed using the techniques disclosedherein, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

Non-limiting embodiments will be described by way of example withreference to the accompanying figures, which are schematic and are notintended to be drawn to scale. In the figures, each identical or nearlyidentical component illustrated is typically represented by a singlenumeral. For purposes of clarity, not every component is labeled inevery figure, nor is every component of each embodiment shown whereillustration is not necessary to allow understanding by those ofordinary skill in the art. In the specification, as well as in theclaims, all transitional phrases such as “comprising,” “including,”“carrying,” “having,” “containing,” “involving,” “holding,” “composedof,” and the like are to be understood to be open-ended, i.e., to meanincluding but not limited to. Only the transitional phrases “consistingof” and “consisting essentially of” shall be closed or semi-closedtransitional phrases, respectively. Further, relative terms, such as“above,” “below,” “top,” “bottom,” “upper” and “lower” are used todescribe the various elements' relationships to one another, asillustrated in the accompanying drawings. It is understood that theserelative terms are intended to encompass different orientations of thedevice and/or elements in addition to the orientation depicted in thedrawings. For example, if the device were inverted with respect to theview in the drawings, an element described as “above” another element,for example, would now be below that element. The term “compensating” isto be understood as including “substantially compensating”. The terms“oppose”, “opposes” and “opposing” are to be understood as including“substantially oppose”, “substantially opposes” and “substantiallyopposing” respectively. Further, as used in the specification andappended claims, and in addition to their ordinary meanings, the terms“substantial” or “substantially” mean to within acceptable limits ordegree. For example, “substantially cancelled” means that one skilled inthe art would consider the cancellation to be acceptable. As used in thespecification and the appended claims and in addition to its ordinarymeaning, the term “approximately” or “about” means to within anacceptable limit or amount to one of ordinary skill in the art. Forexample, “approximately the same” means that one of ordinary skill inthe art would consider the items being compared to be the same. As usedin the specification and appended claims, the terms “a”, “an” and “the”include both singular and plural referents, unless the context clearlydictates otherwise. Thus, for example, “a device” includes one deviceand plural devices. As used herein, the International TelecommunicationUnion (ITU) defines Super High Frequency (SHF) as extending betweenthree Gigahertz (3 GHz) and thirty Gigahertz (30 GHz). The ITU definesExtremely High Frequency (EHF) as extending between thirty Gigahertz (30GHz) and three hundred Gigahertz (300 GHz).

FIG. 1A is a diagram that illustrates an example temperaturecompensating bulk acoustic wave (BAW) resonator structure 100. FIGS. 4Athrough 4G show alternative example temperature compensating bulkacoustic (BAW) wave resonators, 400A through 400G, to the exampletemperature compensating bulk acoustic wave (BAW) resonator structure100 shown in FIG. 1A. The foregoing are shown in simplified crosssectional views. The resonator structures are formed over a substrate101, 401A through 401G (e.g., silicon substrate 101, 401A, 401B, 401Dthrough 401F, e.g., silicon carbide substrate 401C. In some examples,the substrate may further comprise a seed layer 103, 403A, 403B, 403Dthrough 403F, formed of, for example, aluminum nitride (AlN), or anothersuitable material (e.g., silicon dioxide (SiO₂), aluminum oxide (Al₂O₃),silicon nitride (Si₃N₄), amorphous silicon (a-Si), silicon carbide(SiC)), having an example thickness in a range from approximately 100 Ato approximately 1 um on the silicon substrate.

The example temperature compensating bulk acoustic wave (BAW) resonators100, 400A through 400G, may include a respective stack 104, 404A through404G, of an example four layers of temperature compensatingpiezoelectric material, for example, four layers including AluminumNitride (AlN) having a wurtzite structure and also including temperaturecompensating material, e.g., Silicon Dioxide (SiO₂) layer. Thetemperature compensating material may have a positive acoustic velocitytemperature coefficient, so acoustic velocity increases with increasingtemperature of the temperature compensating material. The temperaturecompensating material may facilitate compensating for frequency responseshifts with increasing temperature. Most materials (e.g., metals, e.g.,dielectrics) generally have a negative acoustic velocity temperaturecoefficient, so acoustic velocity decreases with increasing temperatureof such materials. Accordingly, increasing device temperature generallycauses response of resonators and filters to shift downward infrequency. Including dielectric (e.g., silicon dioxide) that instead hasa positive acoustic velocity temperature coefficient may facilitatecountering or compensating (e.g., temperature compensating) thisdownward shift in frequency with increasing temperature.

For example, FIG. 1A and FIGS. 4A through 4G show a bottom temperaturecompensating piezoelectric layer 105, 405A through 405G, a first middletemperature compensating piezoelectric layer 107, 407A through 407G, asecond middle temperature compensating piezoelectric layer 109, 409Athrough 409G, and a top temperature compensating piezoelectric layer111, 411A through 411G. For example, in FIGS. 1A and 4A through 4C,bottom temperature compensating piezoelectric layer 105, 405A through405C may comprise a first pair of sublayers of piezoelectric material105A, 105B, 405AA, 405AB, 405BA, 405BB, 405CA, 405CB, and a first layerof temperature compensating material 159, 459A, 459B, 459C (e.g.,comprising Silicon Dioxide (SiO₂) layer, e.g., comprising metal sublayerover Silicon Dioxide (SiO₂) sublayer) interposed between first andsecond members of the first pair of sublayers of piezoelectric material105A, 105B, 405AA, 405AB, 405BA, 405BB, 405CA, 405CB). Similarly, inFIG. 4D through 4G, bottom temperature compensating piezoelectric layer405D through 405G may comprise a first pair of sublayers ofpiezoelectric material (shown without reference numbers for the sake ofsimplicity), and a first layer of temperature compensating material459D, 459E, 459F, 459G interposed between first and second members ofthe first pair of sublayers of piezoelectric material. For example, inFIGS. 1A and 4A through 4C, first middle temperature compensatingpiezoelectric layer 107, 407A through 407C may comprise a second pair ofsublayers of piezoelectric material 107A, 107B, 407AA, 407AB, 407BA,407BB, 407CA, 407CB, and a second layer of temperature compensatingmaterial 161, 461A, 461B, 461C (e.g., comprising Silicon Dioxide (SiO₂)layer, e.g., comprising metal sublayer over Silicon Dioxide (SiO₂)sublayer) interposed between first and second members of the second pairof sublayers of piezoelectric material 107A, 107B, 407AA, 407AB, 407BA,407BB, 407CA, 407CB. Similarly, in FIG. 4D through 4G, first middletemperature compensating piezoelectric layer 407D through 407G maycomprise a second pair of sublayers of piezoelectric material (shownwithout reference numbers for the sake of simplicity), and a secondlayer of temperature compensating material 461D, 461E, 461F, 461Ginterposed between first and second members of the second pair ofsublayers of piezoelectric material.

For example, in FIGS. 1A and 4A through 4C, second middle temperaturecompensating piezoelectric layer 109, 409A through 409C may comprise athird pair of sublayers of piezoelectric material 109A, 109B, 409AA,409AB, 409BA, 409BB, 409CA, 409CB, and a third layer of temperaturecompensating material 163, 463A, 463B, 463C (e.g., Silicon Dioxide(SiO2) layer) interposed between first and second members of the thirdpair of sublayers of piezoelectric material 109A, 109B, 409AA, 409AB,409BA, 409BB, 409CA, 409CB. Similarly, in FIG. 4D through 4G, secondmiddle temperature compensating piezoelectric layer 409D through 409Gmay comprise a third pair of sublayers of piezoelectric material (shownwithout reference numbers for the sake of simplicity), and a third layerof temperature compensating material 463D, 463E, 463F, 463G interposedbetween first and second members of the third pair of sublayers ofpiezoelectric material. For example, in FIGS. 1A and 4A through 4C, toptemperature compensating piezoelectric layer 111, 411A through 411C maycomprise a fourth pair of sublayers of piezoelectric material 111A,111B, 411AA, 411AB, 411BA, 411BB, 411CA, 411CB, and a fourth layer oftemperature compensating material 164, 464A, 464B, 464C (e.g., SiliconDioxide (SiO₂) layer) interposed between first and second members of thefourth pair of sublayers of piezoelectric material 111A, 111B, 411AA,411AB, 411BA, 411BB, 411CA, 411CB. Similarly, in FIG. 4D through 4G, toptemperature compensating piezoelectric layer 411D through 411G maycomprise a fourth pair of sublayers of piezoelectric material (shownwithout reference numbers for the sake of simplicity), and a fourthlayer of temperature compensating material 464D, 464E, 464F, 464Ginterposed between first and second members of the fourth pair ofsublayers of piezoelectric material. Minimum thickness for the layers oftemperature compensating material just discussed may be about onemono-layer, or about five Angstroms (5 A). It is theorized that if thelayers of temperature compensating material just discussed are too thinthere is no substantial temperature compensating effect. Further, if thelayers of temperature compensating material are too thick, the effectiveelectromechanical coupling coefficient (Kt2) may decrease significantlyand/or undesired rattle strength may increase. Accordingly, an upperlimit of thickness for layers of temperature compensating material maybe about five-hundred Angstroms (500 A) for a twenty-four Gigahertz (24GHz) resonator design, with limiting thickness scaling inversely withfrequency for alternative resonator designs.

A mesa structure 104, 404A through 404G (e.g., first mesa structure 104,404A through 404G) may comprise the respective stack 104, 404A through404G, of the example four layers of temperature compensatingpiezoelectric material. The mesa structure 104, 404A through 404G (e.g.,first mesa structure 104, 404A through 404G) may comprise bottomtemperature compensating piezoelectric layer 105, 405A through 405G. Themesa structure 104, 404A through 404G (e.g., first mesa structure 104,404A through 404G) may comprise first middle temperature compensatingpiezoelectric layer 107, 407A through 407G. The mesa structure 104, 404Athrough 404G (e.g., first mesa structure 104, 404A through 404G) maycomprise second middle temperature compensating piezoelectric layer 109,409A through 409G. The mesa structure 104, 404A through 404G (e.g.,first mesa structure 104, 404A through 404G) may comprise toptemperature compensating piezoelectric layer 111, 411A through 411G.

The four layers of temperature compensating piezoelectric material inthe respective stack 104, 404A through 404G of FIG. 1A and FIGS. 4Athrough 4G may have an alternating axis arrangement in the respectivestack 104, 404A through 404G. For example the bottom temperaturecompensating piezoelectric layer 105, 405A through 405G may have anormal axis orientation (e.g, normal axis TC piezo 105, 405A through405G), which is depicted in the figures using a downward directed arrow.Next in the alternating axis arrangement of the respective stack 104,404A through 404G, the first middle temperature compensatingpiezoelectric layer 107, 407A through 407G may have a reverse axisorientation (e.g, reverse axis TC piezo 107, 407A through 407G), whichis depicted in the figures using an upward directed arrow. Next in thealternating axis arrangement of the respective stack 104, 404A through404G, the second middle temperature compensating piezoelectric layer109, 409A through 409G may have the normal axis orientation (e.g, normalaxis TC piezo 109, 409A through 4059), which is depicted in the figuresusing the downward directed arrow. Next in the alternating axisarrangement of the respective stack 104, 404A through 404G, the toptemperature compensating piezoelectric layer 111, 411A through 411G mayhave the reverse axis orientation (e.g, reverse axis TC piezo 111, 411Athrough 411G), which is depicted in the figures using the upwarddirected arrow.

For example, polycrystalline thin film MN may be grown in acrystallographic c-axis negative polarization, or normal axisorientation perpendicular relative to the substrate surface usingreactive magnetron sputtering of an Aluminum target in a nitrogenatmosphere. However, as will be discussed in greater detail subsequentlyherein, changing sputtering conditions, for example by adding oxygen,may reverse the axis to a crystallographic c-axis positive polarization,or reverse axis, orientation perpendicular relative to the substratesurface.

For example, in FIGS. 1A and 4A through 4C, bottom temperaturecompensating piezoelectric layer 105, 405A through 405C having thenormal axis orientation, which is depicted in the figures using thedownward directed arrow, may comprise the first pair of sublayers ofpiezoelectric material 105A, 105B, 405AA, 405AB, 405BA, 405BB, 405CA,405CB, having the normal axis orientation. Similarly, in FIG. 4D through4G, bottom temperature compensating piezoelectric layer 405D through405G having the normal axis orientation, which is depicted in thefigures using the downward directed arrow may comprise the first pair ofsublayers of piezoelectric material having the normal axis orientation(shown without reference numbers for the sake of simplicity). Forexample, in FIGS. 1A and 4A through 4C, first middle temperaturecompensating piezoelectric layer 107, 407A through 407C having thereverse axis orientation, which is depicted in the figures using theupward directed arrow, may comprise a second pair of sublayers ofpiezoelectric material 107A, 107B, 407AA, 407AB, 407BA, 407BB, 407CA,407CB having the reverse axis orientation. Similarly, in FIG. 4D through4G, first middle temperature compensating piezoelectric layer 407Dthrough 407G having the reverse axis orientation, which is depicted inthe figures using the upward directed arrow, may comprise a second pairof sublayers of piezoelectric material having the reverse axisorientation (shown without reference numbers for the sake ofsimplicity).

For example, in FIGS. 1A and 4A through 4C, second middle temperaturecompensating piezoelectric layer 109, 409A through 409C having thenormal axis orientation, which is depicted in the figures using thedownward directed arrow, may comprise a third pair of sublayers ofpiezoelectric material 109A, 109B, 409AA, 409AB, 409BA, 409BB, 409CA,409CB having the normal axis orientation. Similarly, in FIG. 4D through4G, second middle temperature compensating piezoelectric layer 409Dthrough 409G having the normal axis orientation, which is depicted inthe figures using the downward directed arrow, may comprise a third pairof sublayers of piezoelectric material having the normal axisorientation (shown without reference numbers for the sake ofsimplicity). For example, in FIGS. 1A and 4A through 4C, top temperaturecompensating piezoelectric layer 111, 411A through 411C having thereverse axis orientation, which is depicted in the figures using theupward directed arrow, may comprise a fourth pair of sublayers ofpiezoelectric material 111A, 111B, 411AA, 411AB, 411BA, 411BB, 411CA,411CB having the reverse axis orientation. Similarly, in FIG. 4D through4G, top temperature compensating piezoelectric layer 411D through 411Ghaving the reverse axis orientation, which is depicted in the figuresusing the upward directed arrow, may comprise a fourth pair of sublayersof piezoelectric material having the reverse axis orientation (shownwithout reference numbers for the sake of simplicity).

In the example resonators 100, 400A through 400G, of FIG. 1A and FIGS.4A through 4G, the bottom temperature compensating piezoelectric layer105, 405A through 405G, may have a piezoelectrically excitable resonancemode (e.g., main resonance mode) at a resonant frequency (e.g., mainresonant frequency) of the example resonators. Similarly, the firstmiddle temperature compensating piezoelectric layer 107, 407A through407G, may have its piezoelectrically excitable resonance mode (e.g.,main resonance mode) at the resonant frequency (e.g., main resonantfrequency) of the example resonators. Similarly, the second middletemperature compensating piezoelectric layer 109, 409A through 409G, mayhave its piezoelectrically excitable resonance mode (e.g., mainresonance mode) at the resonant frequency (e.g., main resonantfrequency) of the example resonators. Similarly, the top temperaturecompensating piezoelectric layer 111, 411A through 411G, may have itspiezoelectrically excitable main resonance mode (e.g., main resonancemode) at the resonant frequency (e.g., main resonant frequency) of theexample resonators. Accordingly, the top temperature compensatingpiezoelectric layer 111, 411A through 411G, may have itspiezoelectrically excitable main resonance mode (e.g., main resonancemode) at the resonant frequency (e.g., main resonant frequency) with thebottom temperature compensating piezoelectric layer 105, 405A through405G, the first middle temperature compensating piezoelectric layer 107,407A through 407G, and the second middle temperature compensatingpiezoelectric layer 109, 409A through 409G.

The bottom temperature compensating piezoelectric layer 105, 405Athrough 405G, may be acoustically coupled with the first middletemperature compensating piezoelectric layer 107, 407A through 407G, inthe piezoelectrically excitable resonance mode (e.g., main resonancemode) at the resonant frequency (e.g., main resonant frequency) of theexample resonators 100, 400A through 400G. The normal axis of bottomtemperature compensating piezoelectric layer 105, 405A through 405G, inopposing the reverse axis of the first middle temperature compensatingpiezoelectric layer 107, 407A through 407G, may cooperate for thepiezoelectrically excitable resonance mode (e.g., main resonance mode)at the resonant frequency (e.g., main resonant frequency) of the exampleresonators. The first middle temperature compensating piezoelectriclayer 107, 407A through 407G, may be sandwiched between the bottomtemperature compensating piezoelectric layer 105, 405A through 405G, andthe second middle temperature compensating piezoelectric layer 109, 409Athrough 409G, for example, in the alternating axis arrangement in therespective stack 104, 404A through 404G. For example, the reverse axisof the first middle temperature compensating piezoelectric layer 107,407A through 407G, may oppose the normal axis of the bottom temperaturecompensating piezoelectric layer 105, 405A through 405G, and the normalaxis of the second middle temperature compensating piezoelectric layer109, 409A-409G. In opposing the normal axis of the bottom piezoelectriclayer 105, 405A through 405G, and the normal axis of the second middletemperature compensating piezoelectric layer 109, 409A through 409G, thereverse axis of the first middle temperature compensating piezoelectriclayer 107, 407A through 407G, may cooperate for the piezoelectricallyexcitable resonance mode (e.g., main resonance mode) at the resonantfrequency (e.g., main resonant frequency) of the example resonators.

The second middle temperature compensating piezoelectric layer 109, 409Athrough 409G, may be sandwiched between the first middle temperaturecompensating piezoelectric layer 107, 407A through 407G, and the toptemperature compensating piezoelectric layer 111, 411A through 411G, forexample, in the alternating axis arrangement in the respective stack104, 404A through 404G. For example, the normal axis of the secondmiddle temperature compensating piezoelectric layer 109, 409A through409G, may oppose the reverse axis of the first middle temperaturecompensating piezoelectric layer 107, 407A through 407G, and the reverseaxis of the top temperature compensating piezoelectric layer 111, 411Athrough 411G. In opposing the reverse axis of the first middletemperature compensating piezoelectric layer 107, 407A through 407G, andthe reverse axis of the top temperature compensating piezoelectric layer111, 411A through 411G, the normal axis of the second middle temperaturecompensating piezoelectric layer 109, 409A through 409G, may cooperatefor the piezoelectrically excitable resonance mode (e.g., main resonancemode) at the resonant frequency (e.g., main resonant frequency) of theexample resonators. Similarly, the alternating axis arrangement of thebottom temperature compensating piezoelectric layer 105, 405A through405G, and the first middle temperature compensating piezoelectric layer107, 407A through 407G, and the second middle temperature compensatingpiezoelectric layer 109, 409A through 409G, and the top temperaturecompensating piezoelectric layer 111, 411A-411G, in the respective stack104, 404A through 404G may cooperate for the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the example temperature compensatingbulk acoustic wave (BAW) resonators. Despite differing in theiralternating axis arrangement in the respective stack 104, 404A through404G, the bottom piezoelectric layer 105, 405A through 405G and thefirst middle piezoelectric layer 107, 407A through 407G, and the secondmiddle piezoelectric layer 109, 409A through 409G, and the toppiezoelectric layer 111, 411A through 411G, may all be made of the samepiezoelectric material, e.g., Aluminum Nitride (AlN).

Respective layers of temperature compensating piezoelectric material inthe stack 104, 404A through 404G, of FIG. 1A and FIGS. 4A through 4G mayhave respective layer thicknesses of about one half wavelength (e.g.,one half acoustic wavelength) of the main resonant frequency of theexample resonators. For example, respective layers of temperaturecompensating piezoelectric material in the stack 104, 404A through 404G,of FIG. 1A and FIGS. 4A through 4G may have respective layer thicknessesso that (e.g., selected so that) the respective temperature compensatingbulk acoustic wave resonators 100, 400A through 400G may have respectiveresonant frequencies that are in a Super High Frequency (SHF) band or anExtremely High Frequency (EHF) band (e.g., respective resonantfrequencies that are in a Super High Frequency (SHF) band, e.g.,respective resonant frequencies that are in an Extremely High Frequency(EHF) band.) For example, for a twenty-four gigahertz (e.g., 24 GHz)main resonant frequency of the example resonators, the bottomtemperature compensating piezoelectric layer 105, 405A through 405G, mayhave a layer thickness corresponding to about one half of a wavelength(e.g., about one half of an acoustic wavelength) of the main resonantfrequency, and may be about two thousand Angstroms (2000 A). Similarly,the first middle temperature compensating piezoelectric layer 107, 407Athrough 407G, may have a layer thickness approximately corresponding theone half of the wavelength (e.g., about one half of the acousticwavelength) of the main resonant frequency; the second middletemperature compensating piezoelectric layer 109, 409A through 409G, mayhave a layer thickness approximately corresponding to the one half ofthe wavelength (e.g., about one half of the acoustic wavelength) of themain resonant frequency; and the top temperature compensatingpiezoelectric layer 111, 411A through 411G, may have a layer thicknessapproximately corresponding to the one half of the wavelength (e.g.,about one half of the acoustic wavelength) of the main resonantfrequency. Piezoelectric layer thickness may be scaled up or down todetermine main resonant frequency.

Since the temperature compensating piezoelectric layers may haverespective thicknesses of about one half wavelength (e.g., one halfacoustic wavelength) of the main resonant frequency of the exampleresonators, corresponding members of the pairs of the sublayers may haverespective thicknesses of about one quarter wavelength (e.g., onequarter acoustic wavelength) of the main resonant frequency of theexample resonators. Accordingly, neglecting thickness of the respectivethin interposing layers of temperature compensating material, the tworespective quarter acoustic wave length thick members of the respectivepairs of sublayers may sum thickness together to provide the thicknessesof about one half wavelength (e.g., one half acoustic wavelength) therespective temperature compensating piezoelectric layers. For example,in FIG. 1A and FIGS. 4A-4C, members of the first pair of sublayers ofpiezoelectric material 105A, 105B, 405AA, 405AB, 405BA, 405BB, 405CA,405CB may have respective thicknesses of about one quarter wavelength(e.g., one quarter acoustic wavelength) of the main resonant frequencyof the example temperature compensating resonators. For example, in FIG.1A and FIGS. 4A-4C, members of the second pair of sublayers ofpiezoelectric material 107A, 107B, 407AA, 407AB, 407BA, 407BB, 407CA,407CB may have respective thicknesses of about one quarter wavelength(e.g., one quarter acoustic wavelength) of the main resonant frequencyof the example temperature compensating resonators. For example, in FIG.1A and FIGS. 4A-4C, members of the third pair of sublayers ofpiezoelectric material 109A, 109B, 409AA, 409AB, 409BA, 409BB, 409CA,409CB may have respective thicknesses of about one quarter wavelength(e.g., one quarter acoustic wavelength) of the main resonant frequencyof the example temperature compensating resonators. For example, in FIG.1A and FIGS. 4A-4C, fourth pair of sublayers of piezoelectric material111A, 111B, 411AA, 411AB, 411BA, 411BB, 411CA, 411CB may have respectivethicknesses of about one quarter wavelength (e.g., one quarter acousticwavelength) of the main resonant frequency of the example temperaturecompensating resonators. However, depending on the desired temperaturecompensating (e.g., degree of temperature compensating effect) fortemperature compensating bulk acoustic wave resonators 100, 400A through400G, the thicknesses of sublayers of piezoelectric materials may varyfrom about one tenth to about one quarter wavelength of the mainresonant frequency of the example temperature compensating resonators asshould be appreciated by one skilled in the art.

The example temperature compensating bulk acoustic wave resonators 100,400A through 400G, of FIG. 1A and FIGS. 4A through 4G may comprise: abottom acoustic reflector 113, 413A through 413G, including anacoustically reflective bottom electrode stack of a plurality of bottommetal electrode layers; and a top acoustic reflector 115, 415A through415G, including an acoustically reflective bottom electrode stack of aplurality of top metal electrode layers. Accordingly, the bottomacoustic reflector 113, 413A through 413G, may be a bottom multilayeracoustic reflector, and the top acoustic reflector 115, 415A through415G, may be a top multilayer acoustic reflector. The temperaturecompensating piezoelectric layer stack 104, 404A through 404G, may besandwiched between the plurality of bottom metal electrode layers of thebottom acoustic reflector 113, 413A through 413G, and the plurality oftop metal electrode layers of the top acoustic reflector 115, 415Athrough 415G. The temperature compensating piezoelectric layer stack104, 404A through 404G, may be electrically and acoustically coupledwith the plurality of bottom metal electrode layers of the bottomacoustic reflector 113, 413A through 413G and the plurality of top metalelectrode layers of the top acoustic reflector 115, 415A through 415G,to excite the piezoelectrically excitable resonance mode (e.g., mainresonance mode) at the resonant frequency (e.g., main resonantfrequency). For example, such excitation may be done by using theplurality of bottom metal electrode layers of the bottom acousticreflector 113, 413A through 413G and the plurality of top metalelectrode layers of the top acoustic reflector 115, 415A through 415G toapply an oscillating electric field having a frequency corresponding tothe resonant frequency (e.g., main resonant frequency) of thetemperature compensating piezoelectric layer stack 104, 404A through404G, and of the example temperature compensating bulk acoustic waveresonators 100, 400A through 400G.

For example, the bottom temperature compensating piezoelectric layer105, 405A through 405G, may be electrically and acoustically coupledwith the plurality of bottom metal electrode layers of the bottomacoustic reflector 113, 413A through 413G and the plurality of top metalelectrode layers of the top acoustic reflector 115, 415A through 415G,to excite the piezoelectrically excitable resonance mode (e.g., mainresonance mode) at the resonant frequency (e.g., main resonantfrequency) of the bottom temperature compensating piezoelectric layer105, 405A through 405G. Further, the bottom temperature compensatingpiezoelectric layer 105, 405A through 405G and the first middletemperature compensating piezoelectric layer 107, 407A through 407G, maybe electrically and acoustically coupled with the plurality of bottommetal electrode layers of the bottom acoustic reflector 113, 413Athrough 413G, and the plurality of top metal electrode layers of the topacoustic reflector 115, 415A through 415G, to excite thepiezoelectrically excitable resonance mode (e.g., main resonance mode)at the resonant frequency (e.g., main resonant frequency) of the bottomtemperature compensating piezoelectric layer 105, 405A through 405G,acoustically coupled with the first middle temperature compensatingpiezoelectric layer 107, 407A through 407G. Additionally, the firstmiddle temperature compensating piezoelectric layer 107, 407A-407G, maybe sandwiched between the bottom temperature compensating piezoelectriclayer 105, 405A through 405G and the second middle temperaturecompensating piezoelectric layer 109, 409A through 409G, and may beelectrically and acoustically coupled with the plurality of bottom metalelectrode layers of the bottom acoustic reflector 113, 413A through413G, and the plurality of top metal electrode layers of the topacoustic reflector 115, 415A through 415G, to excite thepiezoelectrically excitable resonance mode (e.g., main resonance mode)at the resonant frequency (e.g., main resonant frequency) of the firstmiddle temperature compensating piezoelectric layer 107, 407A through407G, sandwiched between the bottom temperature compensatingpiezoelectric layer 105, 405A through 405G, and the second middletemperature compensating piezoelectric layer 109, 409A through 409G.

The acoustically reflective bottom electrode stack of the plurality ofbottom metal electrode layers of the bottom acoustic reflector 113, 413Athrough 413G, may have an alternating arrangement of low acousticimpedance metal layer and high acoustic impedance metal layer. Forexample, an initial bottom metal electrode layer 117, 417A through 417G,may comprise a relatively high acoustic impedance metal, for example,Tungsten having an acoustic impedance of about 100 MegaRayls, or forexample, Molybdenum having an acoustic impedance of about 65 MegaRayls.The acoustically reflective bottom electrode stack of the plurality ofbottom metal electrode layers of the bottom acoustic reflector 113, 413Athrough 413G may approximate a metal distributed Bragg acousticreflector. The plurality of metal bottom electrode layers of the bottomacoustic reflector may be electrically coupled (e.g., electricallyinterconnected) with one another. The acoustically reflective bottomelectrode stack of the plurality of bottom metal electrode layers mayoperate together as a multilayer (e.g., bilayer, e.g., multiple layer)bottom electrode for the bottom acoustic reflector 113, 413A through413G.

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective bottom electrode stack, may be a first pair of bottom metalelectrode layers 119, 419A through 419G and 121, 421A through 421G. Afirst member 119, 419A through 419G, of the first pair of bottom metalelectrode layers may comprise a relatively low acoustic impedance metal,for example, Titanium having an acoustic impedance of about 27MegaRayls, or for example, Aluminum having an acoustic impedance ofabout 18 MegaRayls. A second member 121, 421A through 421G, of the firstpair of bottom metal electrode layers may comprise the relatively highacoustic impedance metal, for example, Tungsten or Molybdenum.Accordingly, the first pair of bottom metal electrode layers 119, 419Athrough 419G, and 121, 421A through 421G, of the bottom acousticreflector 113, 413A through 413G, may be different metals, and may haverespective acoustic impedances that are different from one another so asto provide a reflective acoustic impedance mismatch at the resonantfrequency (e.g., main resonant frequency). Similarly, the initial bottommetal electrode layer 117, 417A through 417G, and the first member ofthe first pair of bottom metal electrode layers 119, 419A through 419G,of the bottom acoustic reflector 113, 413A through 413G, may bedifferent metals, and may have respective acoustic impedances that aredifferent from one another so as to provide a reflective acousticimpedance mismatch at the resonant frequency (e.g., main resonantfrequency).

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective bottom electrode stack, a second pair of bottom metalelectrode layers 123, 423A through 423G, and 125, 425A through 425G, mayrespectively comprise the relatively low acoustic impedance metal andthe relatively high acoustic impedance metal. Accordingly, the initialbottom metal electrode layer 117, 417A through 417G, and members of thefirst and second pairs of bottom metal electrode layers 119, 419Athrough 419G, 121, 421A through 421G, 123, 423A through 423G, 125, 425Athrough 425G, may have respective acoustic impedances in the alternatingarrangement to provide a corresponding plurality of reflective acousticimpedance mismatches.

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective bottom electrode stack, a third pair of bottom metalelectrode layers 127, 427D, 129, 429D may respectively comprise therelatively low acoustic impedance metal and the relatively high acousticimpedance metal. Next in the alternating arrangement of low acousticimpedance metal layer and high acoustic impedance metal layer of theacoustically reflective bottom electrode stack, a fourth pair of bottommetal electrode layers 131, 431D and 133, 433D may respectively comprisethe relatively low acoustic impedance metal and the relatively highacoustic impedance metal.

Respective thicknesses of the bottom metal electrode layers may berelated to wavelength (e.g., acoustic wavelength) for the main resonantfrequency of the example temperature compensating bulk acoustic waveresonators, 100, 400A through 400G. Further, various embodiments forresonators having relatively higher resonant frequency (higher mainresonant frequency) may have relatively thinner bottom metal electrodethicknesses, e.g., scaled thinner with relatively higher resonantfrequency (e.g., higher main resonant frequency). Similarly, variousalternative embodiments for resonators having relatively lower resonantfrequency (e.g., lower main resonant frequency) may have relativelythicker bottom metal electrode layer thicknesses, e.g., scaled thickerwith relatively lower resonant frequency (e.g., lower main resonantfrequency). For example, a layer thickness of the initial bottom metalelectrode layer 117, 417A through 417G, may be about one eighth of awavelength (e.g., one eighth of an acoustic wavelength) at the mainresonant frequency of the example resonator. For example, if molybdenumis used as the high acoustic impedance metal and the main resonantfrequency of the resonator is twenty-four gigahertz (e.g., 24 GHz), thenusing the one eighth of the wavelength (e.g., one eighth of the acousticwavelength) provides the layer thickness of the initial bottom metalelectrode layer 117, 417A through 417G, as about three hundred andthirty Angstroms (330 A). In the foregoing example, the one eighth ofthe wavelength (e.g., the one eighth of the acoustic wavelength) at themain resonant frequency was used for determining the layer thickness ofthe initial bottom metal electrode layer 117, 417A-417G, but it shouldbe understood that this layer thickness may be varied to be thicker orthinner in various other alternative example embodiments.

Respective layer thicknesses, T01 through T08, shown in FIG. 1A formembers of the pairs of bottom metal electrode layers may be about anodd multiple (e.g., 1×, 3×, etc.) of a quarter of a wavelength (e.g.,one quarter of the acoustic wavelength) at the main resonant frequencyof the example resonator. However, the foregoing may be varied. Forexample, members of the pairs of bottom metal electrode layers of thebottom acoustic reflector may have respective layer thickness thatcorrespond to from about one eighth to about one half wavelength at theresonant frequency, or an odd multiple (e.g., 1×, 3×, etc.) thereof.

In an example, if Tungsten is used as the high acoustic impedance metal,and the main resonant frequency of the resonator is twenty-fourgigahertz (e.g., 24 GHz), then using the one quarter of the wavelength(e.g., one quarter of the acoustic wavelength) provides the layerthickness of the high impedance metal electrode layer members of thepairs as about five hundred and forty Angstroms (540 A). For example, ifTitanium is used as the low acoustic impedance metal, and the mainresonant frequency of the resonator is twenty-four gigahertz (e.g., 24GHz), then using the one quarter of the wavelength (e.g., one quarter ofthe acoustic wavelength) provides the layer thickness of the lowimpedance metal electrode layer members of the pairs as about sixhundred and thirty Angstroms (630 A). Similarly, respective layerthicknesses for members of the pairs of bottom metal electrode layersshown in FIGS. 4A through 4G may likewise be about one quarter of thewavelength (e.g., one quarter of the acoustic wavelength) of the mainresonant frequency of the example resonator, and these respective layerthicknesses may likewise be determined for members of the pairs ofbottom metal electrode layers for the high and low acoustic impedancemetals employed.

For example, the bottom temperature compensating piezoelectric layer105, 405A through 405G, may be electrically and acoustically coupledwith the initial bottom metal electrode layer 117, 417A through 417G,and pair(s) of bottom metal electrode layers (e.g., first pair of bottommetal electrode layers 119, 419A through 419G, 121, 421A through 421G,e.g., second pair of bottom metal electrode layers 123, 423A through423G, 125, 425A through 425G, e.g., third pair of bottom metal electrodelayers 127, 427D, 129, 429D, fourth pair of bottom metal electrodelayers 131, 431D, 133, 433D), to excite the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the bottom temperature compensatingpiezoelectric layer 105, 405A through 405G. Further, the bottomtemperature compensating piezoelectric layer 105, 405A through 405G andthe first middle temperature compensating piezoelectric layer 107, 407Athrough 407G may be electrically and acoustically coupled with theinitial bottom metal electrode layer 117, 417A through 417G and pair(s)of bottom metal electrode layers (e.g., first pair of bottom metalelectrode layers 119, 419A through 419G, 121, 421A through 421G, e.g.,second pair of bottom metal electrode layers 123, 423A through 423G,125, 425A through 425G, e.g., third pair of bottom metal electrodelayers 127, 427D, 129, 429D), to excite the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the bottom temperature compensatingpiezoelectric layer 105, 405A through 405G acoustically coupled with thefirst middle temperature compensating piezoelectric layer 107, 407Athrough 407G. Additionally, the first middle piezoelectric layer 107,407A through 407G, may be sandwiched between the bottom temperaturecompensating piezoelectric layer 105, 405A through 405G, and the secondmiddle temperature compensating piezoelectric layer 109, 409A through409G, and may be electrically and acoustically coupled with initialbottom metal electrode layer 117, 417A through 417G, and pair(s) ofbottom metal electrode layers (e.g., first pair of bottom metalelectrode layers 119, 419A through 419G, 121, 421A through 421G, e.g.,second pair of bottom metal electrode layers 123, 423A through 423G,125, 425A through 425G, e.g., third pair of bottom metal electrodelayers 127, 427D, 129, 429D), to excite the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the first middle temperaturecompensating piezoelectric layer 107, 407A through 407G, sandwichedbetween the bottom temperature compensating piezoelectric layer 105,405A through 405G, and the second middle temperature compensatingpiezoelectric layer 109, 409A through 409G.

Another mesa structure 113, 413A through 413G, (e.g., second mesastructure 113, 413A through 413G), may comprise the bottom acousticreflector 113, 413A through 413G. The another mesa structure 113, 413Athrough 413G, (e.g., second mesa structure 113, 413A through 413G), maycomprise initial bottom metal electrode layer 117, 417A through 417G.The another mesa structure 113, 413A through 413G, (e.g., second mesastructure 113, 413A through 413G), may comprise one or more pair(s) ofbottom metal electrode layers (e.g., first pair of bottom metalelectrode layers 119, 419A through 419G, 121, 421A through 421G, e.g.,second pair of bottom metal electrode layers 123, 423A through 423G,125, 425A through 425G, e.g., third pair of bottom metal electrodelayers 127, 427A, 427D, 129, 429D, e.g., fourth pair of bottom metalelectrode layers 131, 431D, 133, 433D).

Similar to what has been discussed for the bottom electrode stack,likewise the top electrode stack of the plurality of top metal electrodelayers of the top acoustic reflector 115, 415A through 415G, may havethe alternating arrangement of low acoustic impedance metal layer andhigh acoustic impedance metal layer. For example, an initial top metalelectrode layer 135, 435A through 435G, may comprise the relatively highacoustic impedance metal, for example, Tungsten or Molybdenum. The topelectrode stack of the plurality of top metal electrode layers of thetop acoustic reflector 115, 415A through 415G, may approximate a metaldistributed Bragg acoustic reflector. The plurality of top metalelectrode layers of the top acoustic reflector may be electricallycoupled (e.g., electrically interconnected) with one another. Theacoustically reflective top electrode stack of the plurality of topmetal electrode layers may operate together as a multilayer (e.g.,bilayer, e.g., multiple layer) top electrode for the top acousticreflector 115, 415A through 415G. Next in the alternating arrangement oflow acoustic impedance metal layer and high acoustic impedance metallayer of the acoustically reflective top electrode stack, may be a firstpair of top metal electrode layers 137, 437A through 437G, and 139, 439Athrough 439G. A first member 137, 437A through 437G, of the first pairof top metal electrode layers may comprise the relatively low acousticimpedance metal, for example, Titanium or Aluminum. A second member 139,439A through 439G, of the first pair of top metal electrode layers maycomprise the relatively high acoustic impedance metal, for example,Tungsten or Molybdenum. Accordingly, the first pair of top metalelectrode layers 137, 437A through 437G, 139, 439A through 439G, of thetop acoustic reflector 115, 415A through 415G, may be different metals,and may have respective acoustic impedances that are different from oneanother so as to provide a reflective acoustic impedance mismatch at theresonant frequency (e.g., main resonant frequency). Similarly, theinitial top metal electrode layer 135, 435A through 435G, and the firstmember of the first pair of top metal electrode layers 137, 437A through437G, of the top acoustic reflector 115, 415A through 415G, may bedifferent metals, and may have respective acoustic impedances that aredifferent from one another so as to provide a reflective acousticimpedance mismatch at the resonant frequency (e.g., main resonantfrequency).

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective top electrode stack, a second pair of top metal electrodelayers 141, 441A through 441G, and 143, 443A through 443G, mayrespectively comprise the relatively low acoustic impedance metal andthe relatively high acoustic impedance metal. Accordingly, the initialtop metal electrode layer 135, 435A through 435G, and members of thefirst and second pairs of top metal electrode layers 137, 437A through437G, 139, 439A through 439G, 141, 441A through 441G, 143, 443A through443G, may have respective acoustic impedances in the alternatingarrangement to provide a corresponding plurality of reflective acousticimpedance mismatches.

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective top electrode stack, a third pair of top metal electrodelayers 145, 445A through 445C, and 147, 447A through 447C, mayrespectively comprise the relatively low acoustic impedance metal andthe relatively high acoustic impedance metal. Next in the alternatingarrangement of low acoustic impedance metal layer and high acousticimpedance metal layer of the acoustically reflective top electrodestack, a fourth pair of top metal electrode layers 149, 449A through449C, 151, 451A through 451C, may respectively comprise the relativelylow acoustic impedance metal and the relatively high acoustic impedancemetal.

For example, the bottom temperature compensating piezoelectric layer105, 405A through 405G, may be electrically and acoustically coupledwith the initial top metal electrode layer 135, 435A through 435G, andthe pair(s) of top metal electrode layers (e.g., first pair of top metalelectrode layers 137, 437A through 437G, 139, 439A through 439G, e.g.,second pair of top metal electrode layers 141, 441A through 441G, 143,443A through 443G, e.g., third pair of top metal electrode layers 145,445A through 445C, 147, 447A through 447C), to excite thepiezoelectrically excitable resonance mode (e.g., main resonance mode)at the resonant frequency (e.g., main resonant frequency) of the bottomtemperature compensating piezoelectric layer 105, 405A through 405G.Further, the bottom temperature compensating piezoelectric layer 105,405A through 405G and the first middle temperature compensatingpiezoelectric layer 107, 407A through 407G may be electrically andacoustically coupled with the initial top metal electrode layer 135,435A through 435G and pair(s) of top metal electrode layers (e.g., firstpair of top metal electrode layers 137, 437A through 437G, 139, 439Athrough 439G, e.g., second pair of top metal electrode layers 141, 441Athrough 441G, 143, 443A through 443G, e.g., third pair of top metalelectrode layers 145, 445A through 445C, 147, 447A through 447C), toexcite the piezoelectrically excitable resonance mode (e.g., mainresonance mode) at the resonant frequency (e.g., main resonantfrequency) of the bottom temperature compensating piezoelectric layer105, 405A through 405G acoustically coupled with the first middletemperature compensating piezoelectric layer 107, 407A through 407G.Additionally, the first middle temperature compensating piezoelectriclayer 107, 407A through 407G, may be sandwiched between the bottomtemperature compensating piezoelectric layer 105, 405A through 405G, andthe second middle temperature compensating piezoelectric layer 109, 409Athrough 409G, and may be electrically and acoustically coupled with theinitial top metal electrode layer 135, 435A through 435G, and thepair(s) of top metal electrode layers (e.g., first pair of top metalelectrode layers 137, 437A through 437G, 139, 439A through 439G, e.g.,second pair of top metal electrode layers 141, 441A through 441G, 143,443A through 443G, e.g., third pair of top metal electrode layers 145,445A through 445C, 147, 447A through 447C), to excite thepiezoelectrically excitable resonance mode (e.g., main resonance mode)at the resonant frequency (e.g., main resonant frequency) of the firstmiddle temperature compensating piezoelectric layer 107, 407A through407G, sandwiched between the bottom temperature compensatingpiezoelectric layer 105, 405A through 405G, and the second middletemperature compensating piezoelectric layer 109, 409A through 409G.

Yet another mesa structure 115, 415A through 415G, (e.g., third mesastructure 115, 415A through 415G), may comprise the top acousticreflector 115, 415A through 415G, or a portion of the top acousticreflector 115, 415A through 415G. The yet another mesa structure 115,415A through 415G, (e.g., third mesa structure 115, 415A through 415G),may comprise initial top metal electrode layer 135, 435A through 435G.The yet another mesa structure 115, 415A through 415C, (e.g., third mesastructure 115, 415A through 415C), may comprise one or more pair(s) oftop metal electrode layers (e.g., first pair of top metal electrodelayers 137, 437A through 437C, 139, 439A through 439C, e.g., second pairof top metal electrode layers 141, 441A through 441C, 143, 443A through443C, e.g., third pair of top metal electrode layers 145, 445A through445C, 147, 447A through 447C, e.g., fourth pair of top metal electrodelayers 149, 449A through 449C, 151, 451A through 451C).

Like the respective layer thicknesses of the bottom metal electrodelayers, respective thicknesses of the top metal electrode layers maylikewise be related to wavelength (e.g., acoustic wavelength) for themain resonant frequency of the example temperature compensating bulkacoustic wave resonators, 100, 400A through 400G. Further, variousembodiments for resonators having relatively higher main resonantfrequency may have relatively thinner top metal electrode thicknesses,e.g., scaled thinner with relatively higher main resonant frequency.Similarly, various alternative embodiments for resonators havingrelatively lower main resonant frequency may have relatively thicker topmetal electrode layer thicknesses, e.g., scaled thicker with relativelylower main resonant frequency. Like the layer thickness of the initialbottom metal, a layer thickness of the initial top metal electrode layer135, 435A through 435G, may likewise be about one eighth of thewavelength (e.g., one eighth of the acoustic wavelength) of the mainresonant frequency of the example resonator. For example, if molybdenumis used as the high acoustic impedance metal and the main resonantfrequency of the resonator is twenty-four gigahertz (e.g., 24 GHz), thenusing the one eighth of the wavelength (e.g., one eighth of the acousticwavelength) provides the layer thickness of the initial top metalelectrode layer 135, 435A through 435G, as about three hundred andthirty Angstroms (330 A). In the foregoing example, the one eighth ofthe wavelength (e.g., one eighth of the acoustic wavelength) at the mainresonant frequency was used for determining the layer thickness of theinitial top metal electrode layer 135, 435A-435G, but it should beunderstood that this layer thickness may be varied to be thicker orthinner in various other alternative example embodiments. Respectivelayer thicknesses, T11 through T18, shown in FIG. 1A for members of thepairs of top metal electrode layers may be about an odd multiple (e.g.,1×, 3×, etc.) of a quarter of a wavelength (e.g., one quarter of anacoustic wavelength) of the main resonant frequency of the exampleresonator. Similarly, respective layer thicknesses for members of thepairs of top metal electrode layers shown in FIGS. 4A through 4G maylikewise be about one quarter of a wavelength (e.g., one quarter of anacoustic wavelength) at the main resonant frequency of the exampleresonator multiplied by an odd multiplier (e.g., 1×, 3×, etc.), andthese respective layer thicknesses may likewise be determined formembers of the pairs of top metal electrode layers for the high and lowacoustic impedance metals employed. However, the foregoing may bevaried. For example, members of the pairs of top metal electrode layersof the top acoustic reflector may have respective layer thickness thatcorrespond to from an odd multiple (e.g., 1×, 3×, etc.) of about oneeighth to an odd multiple (e.g., 1×, 3×, etc.) of about one halfwavelength at the resonant frequency.

The bottom acoustic reflector 113, 413A through 413G, may have athickness dimension T23 extending along the stack of bottom electrodelayers. For the example of the 24 GHz resonator, the thickness dimensionT23 of the bottom acoustic reflector may be about five thousandAngstroms (5,000 A). The top acoustic reflector 115, 415A through 415G,may have a thickness dimension T25 extending along the stack of topelectrode layers. For the example of the 24 GHz resonator, the thicknessdimension T25 of the top acoustic reflector may be about five thousandAngstroms (5,000 A). The temperature compensating piezoelectric layerstack 104, 404A through 404G, may have a thickness dimension T27extending along the temperature compensating piezoelectric layer stack104, 404A through 404G. For the example of the 24 GHz resonator, thethickness dimension T27 of the temperature compensating piezoelectriclayer stack may be about eight thousand Angstroms (8,000 A).

In the example temperature compensating bulk acoustic wave resonators100, 400A through 400G, of FIG. 1A and FIGS. 4A through 4G, a notionalheavy dashed line is used in depicting an etched edge region 153, 453Athrough 453G, associated with the example resonators 100, 400A through400G. Similarly, a laterally opposing etched edge region 154, 454Athrough 454G is arranged laterally opposing or opposite from thenotional heavy dashed line depicting the etched edge region 153, 453Athrough 453G. The etched edge region may, but need not, assist withacoustic isolation of the resonators. The etched edge region may, butneed not, help with avoiding acoustic losses for the resonators. Theetched edge region 153, 453A through 453G, (and the laterally opposingetched edge region 154, 454A through 454G) may extend along thethickness dimension T27 of the temperature compensating piezoelectriclayer stack 104, 404A through 404G. The etched edge region 153, 453Athrough 453G, may extend through (e.g., entirely through or partiallythrough) the temperature compensating piezoelectric layer stack 104,404A through 404G. Similarly, the laterally opposing etched edge region154, 454A through 454G may extend through (e.g., entirely through orpartially through) the temperature compensating piezoelectric layerstack 104, 404A through 404G. The etched edge region 153, 453A through453G, (and the laterally opposing etched edge region 154, 454A through454G) may extend through (e.g., entirely through or partially through)the bottom temperature compensating piezoelectric layer 105, 405Athrough 405G. The etched edge region 153, 453A through 453G, (and thelaterally opposing etched edge region 154, 454A through 454G) may extendthrough (e.g., entirely through or partially through) the first middletemperature compensating piezoelectric layer 107, 407A through 407G. Theetched edge region 153, 453A through 453G, (and the laterally opposingetched edge region 154, 454A through 454G) may extend through (e.g.,entirely through or partially through) the second middle temperaturecompensating piezoelectric layer 109, 409A through 409G. The etched edgeregion 153, 453A through 453G, (and the laterally opposing etched edgeregion 154, 454A through 454G) may extend through (e.g., entirelythrough or partially through) the top temperature compensatingpiezoelectric layer 111, 411A through 411G.

The etched edge region 153, 453A through 453G, (and the laterallyopposing etched edge region 154, 454A through 454G) may extend along thethickness dimension T23 of the bottom acoustic reflector 113, 413Athrough 413G. The etched edge region 153, 453A through 453G, (and thelaterally opposing etched edge region 154, 454A through 454G) may extendthrough (e.g., entirely through or partially through) the bottomacoustic reflector 113, 413A through 413G. The etched edge region 153,453A through 453G, (and the laterally opposing etched edge region 154,454A through 454G) may extend through (e.g., entirely through orpartially through) the initial bottom metal electrode layer 117, 417Athrough 417G. The etched edge region 153, 453A through 453G, (and thelaterally opposing etched edge region 154, 454A through 454G) may extendthrough (e.g., entirely through or partially through) the first pair ofbottom metal electrode layers, 119, 419A through 419G, 121, 421A through421G. The etched edge region 153, 453A through 453G (and the laterallyopposing etched edge region 154, 454A through 454G) may extend through(e.g., entirely through or partially through) the second pair of bottommetal electrode layers, 123, 423A through 423G, 125, 425A through 425G.The etched edge region 153, 453A through 453G (and the laterallyopposing etched edge region 154, 454A through 454G) may extend through(e.g., entirely through or partially through) the third pair of bottommetal electrode layers, 127, 427D, 129, 429D. The etched edge region153, 453A through 453G (and the laterally opposing etched edge region154, 454A through 454G) may extend through (e.g., entirely through orpartially through) the fourth pair of bottom metal electrode layers,131, 431D, 133, 433D.

The etched edge region 153, 453A through 453G (and the laterallyopposing etched edge region 154, 454A through 454G) may extend along thethickness dimension T25 of the top acoustic reflector 115, 415A through415G. The etched edge region 153, 453A through 453G (and the laterallyopposing etched edge region 154, 454A through 454G) may extend through(e.g., entirely through or partially through) the top acoustic reflector115, 415A through 415G. The etched edge region 153, 453A through 453G(and the laterally opposing etched edge region 154, 454A through 454G)may extend through (e.g., entirely through or partially through) theinitial top metal electrode layer 135, 435A through 435G. The etchededge region 153, 453A through 453G (and the laterally opposing etchededge region 154, 454A through 454G) may extend through (e.g., entirelythrough or partially through) the first pair of top metal electrodelayers, 137, 437A through 437G, 139, 439A through 49G. The etched edgeregion 153, 453A through 453C (and the laterally opposing etched edgeregion 154, 454A through 454C) may extend through (e.g., entirelythrough or partially through) the second pair of top metal electrodelayers, 141, 441A through 441C, 143, 443A through 443C. The etched edgeregion 153, 453A through 453C (and the laterally opposing etched edgeregion 154, 454A through 454C) may extend through (e.g., entirelythrough or partially through) the third pair of top metal electrodelayers, 145, 445A through 445C, 147, 447A through 447C. The etched edgeregion 153, 453A through 453C (and the laterally opposing etched edgeregion 154, 454A through 454C) may extend through (e.g., entirelythrough or partially through) the fourth pair of top metal electrodelayers, 149, 449A through 449C, 151, 451A through 451C.

As mentioned previously, mesa structure 104, 404A through 404G (e.g.,first mesa structure 104, 404A through 404G) may comprise the respectivestack 104, 404A through 404G, of the example four layers ofpiezoelectric material. The mesa structure 104, 404A through 404G (e.g.,first mesa structure 104, 404A through 404G) may extend laterallybetween (e.g., may be formed between) etched edge region 153, 453Athrough 453G and laterally opposing etched edge region 154, 454A through454G. As mentioned previously, another mesa structure 113, 413A through413G, (e.g., second mesa structure 113, 413A through 413G), may comprisethe bottom acoustic reflector 113, 413A through 413G. The another mesastructure 113, 413A through 413G, (e.g., second mesa structure 113, 413Athrough 413G) may extend laterally between (e.g., may be formed between)etched edge region 153, 453A through 453G and laterally opposing etchededge region 154, 454A through 454G. As mentioned previously, yet anothermesa structure 115, 415A through 415G, (e.g., third mesa structure 115,415A through 415G), may comprise the top acoustic reflector 115, 415Athrough 415G or a portion of the top acoustic reflector 115, 415Athrough 415G. The yet another mesa structure 115, 415A through 415G,(e.g., third mesa structure 115, 415A through 415G) may extend laterallybetween (e.g., may be formed between) etched edge region 153, 453Athrough 453G and laterally opposing etched edge region 154, 454A through454G. In some example resonators 100, 400A, 400B, 400D through 400F, thesecond mesa structure corresponding to the bottom acoustic reflector113, 413A, 413B, 413D through 413F may be laterally wider than the firstmesa structure corresponding to the stack 104, 404A, 404B, 404D through404F, of the example four layers of piezoelectric material. In someexample resonators 100, 400A through 400C, the first mesa structurecorresponding to the stack 104, 404A through 404C, of the example fourlayers of piezoelectric material may be laterally wider than the thirdmesa structure corresponding to the top acoustic reflector 115, 415Athrough 415C. In some example resonators 400D through 400G, the firstmesa structure corresponding to the stack 404D through 404G, of theexample four layers of piezoelectric material may be laterally widerthan a portion of the third mesa structure corresponding to the topacoustic reflector 415D through 415G.

An optional mass load layer 155, 455A through 455G, may be added to theexample temperature compensating bulk acoustic wave resonators 100, 400Athrough 400G. For example, filters may include series connectedresonator designs and shunt connected resonator designs that may includemass load layers. For example, for ladder filter designs, the shuntresonator may include a sufficient mass load layer so that the parallelresonant frequency (Fp) of the shunt resonator approximately matches theseries resonant frequency (Fs) of the series resonator design. Thus theseries resonator design (without the mass load layer) may be used forthe shunt resonator design, but with the addition of the mass load layer155, 455A through 455G, for the shunt resonator design. By including themass load layer, the design of the shunt resonator may be approximatelydownshifted, or reduced, in frequency relative to the series resonatorby a relative amount approximately corresponding to theelectromechanical coupling coefficient (Kt2) of the shunt resonator. Forthe example resonators 100, 400A through 400G, the optional mass loadlayer 155, 455A through 455G, may be arranged in the top acousticreflector 115, 415A through 415G, above the first pair of top metalelectrode layers. A metal may be used for the mass load. A dense metalsuch as Tungsten may be used for the mass load 155, 455A through 455G.An example thickness dimension of the optional mass load layer 155, 455Athrough 455G, may be about one hundred Angstroms (100 A).

However, it should be understood that the thickness dimension of theoptional mass load layer 155, 455A through 455G, may be varied dependingon how much mass loading is desired for a particular design anddepending on which metal is used for the mass load layer. Since theremay be less acoustic energy in the top acoustic reflector 115, 415Athrough 415G, at locations further away from the piezoelectric stack104, 404A through 404G, there may be less acoustic energy interactionwith the optional mass load layer, depending on the location of the massload layer in the arrangement of the top acoustic reflector.Accordingly, in alternative arrangements where the mass load layer isfurther away from the piezoelectric stack 104, 404A through 404G, suchalternative designs may use more mass loading (e.g., thicker mass loadlayer) to achieve the same effect as what is provided in more proximatemass load placement designs. Also, in other alternative arrangements themass load layer may be arranged relatively closer to the piezoelectricstack 104, 404A through 404G. Such alternative designs may use less massloading (e.g., thinner mass load layer). This may achieve the same orsimilar mass loading effect as what is provided in previously discussedmass load placement designs, in which the mass load is arranged lessproximate to the piezoelectric stack 104, 404A through 404G. Similarly,since Titanium (Ti) or Aluminum (Al) is less dense than Tungsten (W) orMolybdenum (Mo), in alternative designs where Titanium or Aluminum isused for the mass load layer, a relatively thicker mass load layer ofTitanium (Ti) or Aluminum (Al) is needed to produce the same mass loadeffect as a mass load layer of Tungsten (W) or Molybdenum (Mo) of agiven mass load layer thickness. Moreover, in alternative arrangementsboth shunt and series resonators may be additionally mass-loaded withconsiderably thinner mass loading layers (e.g., having thickness ofabout one tenth of the thickness of a main mass loading layer) in orderto achieve specific filter design goals, as may be appreciated by oneskilled in the art.

The example temperature compensating bulk acoustic wave resonators 100,400A through 400G, of FIG. 1A and FIGS. 4A through 4G may include aplurality of lateral features 157, 457A through 457G (e.g., patternedlayer 157, 457A through 457G, e.g., step mass features 157, 457A through457G), sandwiched between two top metal electrode layers (e.g., betweenthe second member 139, 439A through 439G, of the first pair of top metalelectrode layers and the first member 141, 441A through 441G, of thesecond pair of top metal electrode layers) of the top acoustic reflector115, 415A through 415G. As shown in the figures, the plurality oflateral features 157, 457A through 457G, of patterned layer 157, 457Athrough 457G may comprise step features 157, 457A through 457G (e.g.,step mass features 157, 457A through 457G). As shown in the figures, theplurality of lateral features 157, 457A through 457G, may be arrangedproximate to lateral extremities (e.g., proximate to a lateralperimeter) of the top acoustic reflector 115, 415A through 415G. Atleast one of the lateral features 157, 457A through 457G, may bearranged proximate to where the etched edge region 153, 453A through453G, extends through the top acoustic reflector 115, 415A through 415G.

After the lateral features 157, 457A through 457G, are formed, they mayfunction as a step feature template, so that subsequent top metalelectrode layers formed on top of the lateral features 157, 457A through457G, may retain step patterns imposed by step features of the lateralfeatures 157, 457A through 457G. For example, the second pair of topmetal electrode layers 141, 441A through 441G, 143, 443A through 443G,the third pair of top metal electrode layers 145, 445A through 445C,147, 447A through 447C, and the fourth pair of top metal electrodes 149,449A through 449C, 151, 451A through 451C, may retain step patternsimposed by step features of the lateral features 157, 457A through 457G.The plurality of lateral features 157, 457A through 457G, may add alayer of mass loading. The plurality of lateral features 157, 457Athrough 457G, may be made of a patterned metal layer (e.g., a patternedlayer of Tungsten (W), Molybdenum (Mo), Titanium (Ti) or Aluminum (Al)).In alternative examples, the plurality of lateral features 157, 457Athrough 457G, may be made of a patterned dielectric layer (e.g., apatterned layer of Silicon Nitride (SiN), Silicon Dioxide (SiO₂) orSilicon Carbide (SiC)). The plurality of lateral features 157, 457Athrough 457G, may, but need not, limit parasitic lateral acoustic modes(e.g., facilitate suppression of spurious modes) of the exampleresonators 100, 400A through 400G. Thickness of the patterned layer ofthe lateral features 157, 457A through 457G (e.g., thickness of thepatterned layers 157, 457A through 457G), may be adjusted. For example,for the 24 GHz resonator, thickness may be adjusted within a range fromabout fifty Angstroms (50 A) to about five hundred Angstroms (500 A).Lateral step width of the lateral features 157, 457A through 457G (e.g.,width of the step mass features 157, 457A through 457G) may be adjusteddown, for example, from about two microns (2 um). The foregoing may beadjusted to balance a design goal of limiting parasitic lateral acousticmodes (e.g., facilitating suppression of spurious modes) of the exampleresonators 100, 400A through 400G as well as increasing average qualityfactor above the series resonance frequency against other designconsiderations e.g., maintaining desired average quality factor belowthe series resonance frequency.

In the example bulk acoustic wave resonator 100 shown in FIG. 1A, thepatterned layer 157 may comprise Tungsten (W) (e.g., the step massfeature 157 of the patterned layer may comprise Tungsten (W)). Asuitable thickness of the patterned layer 157 (e.g., thickness of thestep mass feature 157) and lateral width of features of the patternedlayer 157 may vary based on various design parameters e.g., materialselected for the patterned layer 157, e.g., the desired resonantfrequency of the given resonant design, e.g., effectiveness infacilitating spurious mode suppression. For the example 24 GHz bulkacoustic wave resonator 100 shown in FIG. 1A in which the patternedlayer comprises Tungsten (W), a suitable thickness of the patternedlayer 157 (e.g., thickness of the step mass feature 157) may be 200Angstroms and lateral width of features of the patterned layer 157(e.g., lateral width of the step mass feature 157) may be 0.8 microns,may facilitate suppression of the average strength of the spurious modesin the passband by approximately fifty percent (50%), as estimated bysimulation relative to similar designs without the benefit of patternedlayer 157.

The example temperature compensating bulk acoustic wave resonators 100,400A through 400G, of FIG. 1A and FIGS. 4A through 4G may include firstinterposer layer 166A, 466A through 466G sandwiched between temperaturecompensating piezoelectric layers of the stack 104, 404A through 404G.For example, first interposer layer 166A, 466A through 466G, may besandwiched between the first middle temperature compensatingpiezoelectric layer 107, 407A through 407G, and the second middletemperature compensating piezoelectric layer 109, 409A through 409G.

The first interposer layer 166A, 466A through 466G may be a first metalinterposer layer 166A, 466A through 466G. The first metal interposerlayer 166A, 466A through 466G may be relatively high acoustic impedancefirst metal interposer layer (e.g., using relatively high acousticimpedance metals such as Tungsten (W) or Molybdenum (Mo)). Such firstmetal interposer layer 166A, 466A through 466G may (but need not)flatten stress distribution across adjacent temperature compensatingpiezoelectric layers, and may (but need not) raise effectiveelectromechanical coupling coefficient (Kt2) of adjacent temperaturecompensating piezoelectric layers.

Alternatively or additionally, the first interposer layer 166A, 466Athrough 466G may be a first dielectric interposer layer 166A, 466Athrough 466G. The dielectric of the first dielectric interposer layer166A, 466A through 466G may be a dielectric that has a positive acousticvelocity temperature coefficient, so acoustic velocity increases withincreasing temperature of the dielectric. The dielectric of the firstdielectric interposer layer 166A, 466A through 466G may be, for example,Silicon Dioxide. The first dielectric interposer layer 166A, 466Athrough 466G may, but need not, facilitate compensating for frequencyresponse shifts with increasing temperature. As mention previously, mostmaterials (e.g., metals, e.g., dielectrics) generally have a negativeacoustic velocity temperature coefficient, so acoustic velocitydecreases with increasing temperature of such materials. Accordingly,increasing device temperature generally causes response of resonatorsand filters to shift downward in frequency. Including dielectric (e.g.,silicon dioxide) that instead has a positive acoustic velocitytemperature coefficient may facilitate countering or compensating (e.g.,temperature compensating) this downward shift in frequency withincreasing temperature. Alternatively or additionally, one or more(e.g., one or a plurality of) interposer layers may comprise metal anddielectric for respective interposer layers. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may comprise different metals for respective interposer layers.Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may comprise different dielectrics for respectiveinterposer layers.

In addition to the foregoing application of metal interposer layers toraise effective electromechanical coupling coefficient (Kt2) of adjacenttemperature compensating piezoelectric layers, and the application ofdielectric interposer layers to facilitate compensating for frequencyresponse shifts with increasing temperature, interposer layers may, butneed not, increase quality factor (Q-factor) and/or suppress irregularspectral response patterns characterized by sharp reductions in Q-factorknown as “rattles”. Q-factor of a resonator is a figure of merit inwhich increased Q-factor indicates a lower rate of energy loss per cyclerelative to the stored energy of the resonator. Increased Q-factor inresonators used in filters results in lower insertion loss and sharperroll-off in filters. The irregular spectral response patternscharacterized by sharp reductions in Q-factor known as “rattles” maycause ripples in filter pass bands.

Metal and/or dielectric interposer layer of suitable thicknesses andacoustic material properties (e.g., velocity, density) may be placed atappropriate places in the stack 104, 404A through 404G, of temperaturecompensating piezoelectric layers, for example, proximate to the nullsof acoustic energy distribution in the stacks (e.g., between interfacesof temperature compensating piezoelectric layers of opposing axisorientation). Finite Element Modeling (FEM) simulations and varyingparameters in fabrication prior to subsequent testing may help tooptimize interposer layer designs for the stack. Thickness of interposerlayers may, but need not, be adjusted to influence increased Q-factorand/or rattle suppression. It is theorized that if the interposer layeris too thin there is no substantial effect. Thus minimum thickness forthe interposer layer may be about one mono-layer, or about fiveAngstroms (5 A). Alternatively, if the interposer layer is too thick,rattle strength may increase rather than being suppressed. Accordingly,an upper limit of interposer thickness may be about five-hundredAngstroms (500 A) for a twenty-four Gigahertz (24 GHz) resonator design,with limiting thickness scaling inversely with frequency for alternativeresonator designs. It is theorized that below a series resonantfrequency of resonators, Fs, Q-factor may not be systematically andsignificantly affected by including a single interposer layer. However,it is theorized that there may, but need not, be significant increasesin Q-factor, for example from about two-thousand (2000) to aboutthree-thousand (3000), for inclusion of two or more interposer layers.

In the example resonators 100, 400A through 400C, of FIG. 1A and FIGS.4A through 4C, a planarization layer 165, 465A through 465C may beincluded. A suitable material may be used for planarization layer 165,465A through 465C, for example Silicon Dioxide (SiO₂), Hafnium Dioxide(HfO2), polyimide, or BenzoCyclobutene (BCB). An isolation layer 167,467A through 467C, may also be included and arranged over theplanarization layer 165, 465A-465C. A suitable low dielectric constant(low-k), low acoustic impedance (low-Za) material may be used for theisolation layer 167, 467A through 467C, for example polyimide, orBenzoCyclobutene (BCB).

In the example resonators 100, 400A through 400G, of FIG. 1A and FIGS.4A through 4G, a bottom electrical interconnect 169, 469A through 469G,may be included to interconnect electrically with (e.g., electricallycontact with) the bottom acoustic reflector 113, 413A through 413G,stack of the plurality of bottom metal electrode layers. A topelectrical interconnect 171, 471A through 471G, may be included tointerconnect electrically with the top acoustic reflector 115, 415Athrough 415G, stack of the plurality of top metal electrode layers. Asuitable material may be used for the bottom electrical interconnect169, 469A through 469G, and the top electrical interconnect 171, 471Athrough 471G, for example, gold (Au). Top electrical interconnect 171,471A through 471G may be substantially acoustically isolated from thestack 104, 404A through 404G of the example four layers of piezoelectricmaterial by the top multilayer metal acoustic reflector electrode 115,415A through 415G. Top electrical interconnect 171, 471A through 471Gmay have dimensions selected so that the top electrical interconnect171, 471A through 471G approximates a fifty ohm electrical transmissionline at the main resonant frequency of the bulk acoustic wave resonator100, 400A through 400G. Top electrical interconnect 171, 471A through471G may have a thickness that is substantially thicker than a thicknessof a pair of top metal electrode layers of the top multilayer metalacoustic reflector electrode 115, 415A through 415G (e.g., thicker thanthickness of the first pair of top metal electrode layers 137, 437Athrough 437G, 139, 439A through 439G). Top electrical interconnect 171,471A through 471G may have a thickness within a range from about onehundred Angstroms (100 A) to about five micrometers (5 um). For example,top electrical interconnect 171, 471A through 471G may have a thicknessof about two thousand Angstroms (2000 A).

FIG. 1B is a simplified view of FIG. 1A that illustrates an example ofacoustic stress distribution during electrical operation of thetemperature compensating bulk acoustic wave resonator structure shown inFIG. 1A. A notional curved line schematically depicts vertical (Tzz)stress distribution 173 through stack 104 of the example fourtemperature compensating piezoelectric layers, 105, 107, 109, 111. Thestress 173 is excited by the oscillating electric field applied via thetop acoustic reflector 115 stack of the plurality of top metal electrodelayers 135, 137, 139, 141, 143, 145, 147, 149, 151, and the bottomacoustic reflector 113 stack of the plurality of bottom metal electrodelayers 117, 119, 121, 123, 125, 127, 129, 131, 133. The stress 173 mayhave maximum values inside the stack 104 of temperature compensatingpiezoelectric layers, while exponentially tapering off within the topacoustic reflector 115 and the bottom acoustic reflector 113. Notably,acoustic energy confined in the resonator structure 100 is proportionalto stress magnitude.

As discussed previously herein, the example four temperaturecompensating piezoelectric layers, 105, 107, 109, 111 in the stack 104may have an alternating axis arrangement in the stack 104. For examplethe bottom temperature compensating piezoelectric layer 105 may have thenormal axis orientation, which is depicted in FIG. 1B using the downwarddirected arrow. Next in the alternating axis arrangement of the stack104, the first middle temperature compensating piezoelectric layer 107may have the reverse axis orientation, which is depicted in FIG. 1Busing the upward directed arrow. Next in the alternating axisarrangement of the stack 104, the second middle temperature compensatingpiezoelectric layer 109 may have the normal axis orientation, which isdepicted in FIG. 1B using the downward directed arrow. Next in thealternating axis arrangement of the stack 104, the top temperaturecompensating piezoelectric layer 111 may have the reverse axisorientation, which is depicted in FIG. 1B using the upward directedarrow. For the alternating axis arrangement of the stack 104, stress 173excited by the applied oscillating electric field causes normal axistemperature compensating piezoelectric layers (e.g., bottom and secondmiddle temperature compensating piezoelectric layers 105, 109) to be incompression, while reverse axis temperature compensating piezoelectriclayers (e.g., first middle and top temperature compensatingpiezoelectric layers 107, 111) to be in extension. Accordingly, FIG. 1Bshows peaks of stress 173 on the right side of the heavy dashed line todepict compression in normal axis temperature compensating piezoelectriclayers (e.g., bottom and second middle temperature compensatingpiezoelectric layers 105, 109), while peaks of stress 173 are shown onthe left side of the heavy dashed line to depict extension in reverseaxis temperature compensating piezoelectric layers (e.g., first middleand top piezoelectric layers 107, 111). As shown, respective layers oftemperature compensating material 159, 161, 163, 164 may be centrallyarranged within respective temperature compensating piezoelectriclayers, 105, 107, 109, 111 proximate to respective peaks of stress,e.g., proximate to respective peaks of acoustic energy. This proximatearrangement may, but need not, enhance interaction between therespective layers of temperature compensating material 159, 161, 163,164 and respective peaks of stress, e.g., respective peaks of acousticenergy, e.g., respective acoustic energy interaction peaks. This in turnmay, but need not, facilitate more substantial temperature compensatingeffect of the respective layers of temperature compensating material159, 161, 163, 164. In contrast, interposer layer 166 may be arranged ata stress null (e.g., acoustic energy null, e.g., acoustic energyinteraction null), interposed between adjacent half wavelength thicknesspiezoelectric layers. In cases where interposer layer 166 may includetemperature compensating material, e.g., Silicon Dioxide (SiO₂), thisarrangement of interposer 166 at the stress null (e.g., acoustic energynull, e.g., acoustic energy interaction null), interposed betweenadjacent half wavelength thickness piezoelectric layers, may result inrelatively less temperature compensating effect of the interposer layer166. In comparison, there may be relatively greater temperaturecompensating effect for layers of temperature compensating material 159,161, 163, 164 arranged at respective peaks of stress, e.g., respectivepeaks of acoustic energy, e.g., respective acoustic energy interactionpeaks for substantially similar thicknesses of temperature compensatingmaterial 159, 161, 163, 164.

FIG. 1C shows a simplified top plan view of a bulk acoustic waveresonator structure 100A corresponding to the cross sectional view ofFIG. 1A, and also shows another simplified top plan view of analternative bulk acoustic wave resonator structure 100B. The bulkacoustic wave resonator structure 100A may include the stack 104A offour layers of piezoelectric material e.g., having the alternatingpiezoelectric axis arrangement of the four layers of piezoelectricmaterial. The stack 104A of piezoelectric layers may be sandwichedbetween the bottom acoustic reflector electrode 113A and the topacoustic reflector electrode 115A. The bottom acoustic reflectorelectrode may comprise the stack of the plurality of bottom metalelectrode layers of the bottom acoustic reflector electrode 113A, e.g.,having the alternating arrangement of low acoustic impedance bottommetal electrode layers and high acoustic impedance bottom metal layers.Similarly, the top acoustic reflector electrode 115A may comprise thestack of the plurality of top metal electrode layers of the top acousticreflector electrode 115A, e.g., having the alternating arrangement oflow acoustic impedance top metal electrode layers and high acousticimpedance top metal electrode layers. The top acoustic reflectorelectrode 115A may include a patterned layer 157A. The patterned layer157A may approximate a frame shape (e.g., rectangular frame shape)proximate to a perimeter (e.g., rectangular perimeter) of top acousticreflector electrode 115A as shown in simplified top plan view in FIG.1C. This patterned layer 157A, e.g., approximating the rectangular frameshape in the simplified top plan view in FIG. 1C, corresponds to thepatterned layer 157 shown in simplified cross sectional view in FIG. 1A.Top electrical interconnect 171A extends over (e.g., electricallycontacts) top acoustic reflector electrode 115A. Bottom electricalinterconnect 169A extends over (e.g., electrically contacts) bottomacoustic reflector electrode 113A through bottom via region 168A.

FIG. 1C also shows another simplified top plan view of an alternativebulk acoustic wave resonator structure 100B. Similarly, the bulkacoustic wave resonator structure 100B may include the stack 104B offour layers of piezoelectric material e.g., having the alternatingpiezoelectric axis arrangement of the four layers of piezoelectricmaterial. The stack 104B of piezoelectric layers may be sandwichedbetween the bottom acoustic reflector electrode 113B and the topacoustic reflector electrode 115B. The bottom acoustic reflectorelectrode may comprise the stack of the plurality of bottom metalelectrode layers of the bottom acoustic reflector electrode 113B, e.g.,having the alternating arrangement of low acoustic impedance bottommetal electrode layers and high acoustic impedance bottom metal layers.Similarly, the top acoustic reflector electrode 115B may comprise thestack of the plurality of top metal electrode layers of the top acousticreflector electrode 115B, e.g., having the alternating arrangement oflow acoustic impedance top metal electrode layers and high acousticimpedance top metal electrode layers. The top acoustic reflectorelectrode 115B may include a patterned layer 157B. The patterned layer157B may approximate a frame shape (e.g., apodized frame shape)proximate to a perimeter (e.g., apodized perimeter) of top acousticreflector electrode 115B as shown in simplified top plan view in FIG.1C. The apodized frame shape may be a frame shape in which substantiallyopposing extremities are not parallel to one another. This patternedlayer 157B, e.g., approximating the apodized frame shape in thesimplified top plan view in FIG. 1C, is an alternative embodimentcorresponding to the patterned layer 157 shown in simplified crosssectional view in FIG. 1A. Top electrical interconnect 171B extends over(e.g., electrically contacts) top acoustic reflector electrode 115B.Bottom electrical interconnect 169B extends over (e.g., electricallycontacts) bottom acoustic reflector electrode 113B through bottom viaregion 168B.

FIG. 1D is a perspective view of an illustrative model of a crystalstructure of AlN in piezoelectric material of layers in FIG. 1A havingreverse axis orientation of negative polarization. Reverse axis AluminumNitride (AlN) may be a used in as the reverse axis piezoelectricmaterial in the sublayers of reverse axis piezoelectric material. Thesereverse axis sublayers of reverse axis piezoelectric material, togetherwith an interposing layer of temperature compensating material (e.g.,Silicon Dioxide (SiO₂)) may comprise the reverse axis temperaturecompensating layer as discussed previously herein. FIG. 1E is aperspective view of an illustrative model of a crystal structure of AlNin piezoelectric material of layers in FIG. 1A having normal axisorientation of positive polarization. Normal axis Aluminum Nitride (AlN)may be a used in as the normal axis piezoelectric material in thesublayers of normal axis piezoelectric material. These normal axissublayers of normal axis piezoelectric material, together with aninterposing layer of temperature compensating material (e.g., SiliconDioxide (SiO2)) may comprise the normal axis temperature compensatinglayer as discussed previously herein. In FIGS. 1D and 1E, Nitrogen (N)atoms are depicted with a hatching style, while Aluminum (Al) atoms aredepicted without a hatching style. FIG. 1D is a perspective view of anillustrative model of a reverse axis crystal structure 175 of AluminumNitride, AlN, in piezoelectric material of layers in FIG. 1A, e.g.,having reverse axis orientation of negative polarization. For example,first middle and top temperature compensating piezoelectric layers 107,111 discussed previously herein with respect to FIGS. 1A and 1B arereverse axis temperature compensating piezoelectric layers. Byconvention, when the first layer of normal axis crystal structure 175 isa Nitrogen, N, layer and second layer in an upward direction (in thedepicted orientation) is an Aluminum, Al, layer, the piezoelectricmaterial including the reverse axis crystal structure 175 is said tohave crystallographic c-axis negative polarization, or reverse axisorientation as indicated by the upward pointing arrow 177. For example,polycrystalline thin film Aluminum Nitride, AlN, may be grown in thecrystallographic c-axis negative polarization, or reverse axis,orientation perpendicular relative to the substrate surface usingreactive magnetron sputtering of an aluminum target in a nitrogenatmosphere, and by introducing oxygen into the gas atmosphere of thereaction chamber during fabrication at the position where the flip tothe reverse axis is desired. An inert gas, for example, Argon may alsobe included in a sputtering gas atmosphere, along with the nitrogen andoxygen.

For example, a predetermined amount of oxygen containing gas may beadded to the gas atmosphere over a short predetermined period of time orfor the entire time the reverse axis layer is being deposited. Theoxygen containing gas may be diatomic oxygen containing gas, such asoxygen (O2). Proportionate amounts of the Nitrogen gas (N2) and theinert gas may flow, while the predetermined amount of oxygen containinggas flows into the gas atmosphere over the predetermined period of time.For example, N2 and Ar gas may flow into the reaction chamber inapproximately a 3:1 ratio of N2 to Ar, as oxygen gas also flows into thereaction chamber. For example, the predetermined amount of oxygencontaining gas added to the gas atmosphere may be in a range from abouta thousandth of a percent (0.001%) to about ten percent (10%), of theentire gas flow. The entire gas flow may be a sum of the gas flows ofargon, nitrogen and oxygen, and the predetermined period of time duringwhich the predetermined amount of oxygen containing gas is added to thegas atmosphere may be in a range from about a quarter (0.25) second to alength of time needed to create an entire layer, for example. Forexample, based on mass-flows, the oxygen composition of the gasatmosphere may be about 2 percent when the oxygen is briefly injected.This results in an aluminum oxynitride (ALON) portion of the finalmonolithic piezoelectric layer, integrated in the Aluminum Nitride, AlN,material, having a thickness in a range of about 5 nm to about 20 nm,which is relatively oxygen rich and very thin. Alternatively, the entirereverse axis piezoelectric layer may be aluminum oxynitride.

FIG. 1E is a perspective view of an illustrative model of a normal axiscrystal structure 179 of Aluminum Nitride, AlN, in piezoelectricmaterial of layers in FIG. 1A, e.g., having normal axis orientation ofpositive polarization. For example, bottom and second middle temperaturecompensating piezoelectric layers 105, 109 discussed previously hereinwith respect to FIGS. 1A and 1B are normal axis piezoelectric layers. Byconvention, when the first layer of the reverse axis crystal structure179 is an Al layer and second layer in an upward direction (in thedepicted orientation) is an N layer, the piezoelectric materialincluding the reverse axis crystal structure 179 is said to have ac-axis positive polarization, or normal axis orientation as indicated bythe downward pointing arrow 181. For example, polycrystalline thin filmMN may be grown in the crystallographic c-axis positive polarization, ornormal axis, orientation perpendicular relative to the substrate surfaceby using reactive magnetron sputtering of an Aluminum target in anitrogen atmosphere.

FIGS. 2A and 2B show a further simplified view of a temperaturecompensating bulk acoustic wave resonator similar to the temperaturecompensating bulk acoustic wave resonator structure shown in FIG. 1Aalong with its corresponding impedance versus frequency response duringits electrical operation, as well as alternative temperaturecompensating bulk acoustic wave resonator structures with differingnumbers of alternating axis temperature compensating piezoelectriclayers, and their respective corresponding impedance versus frequencyresponse during electrical operation. FIG. 2C shows additionalalternative temperature compensating bulk acoustic wave resonatorstructures with additional numbers of alternating axis piezoelectriclayers. Temperature compensating bulk acoustic wave resonators 2001Athrough 2001I may, but need not be, temperature compensating bulkacoustic millimeter wave resonators 2001A through 2001I, operable with amain resonance mode having a main resonant frequency that is amillimeter wave frequency (e.g., twenty-four Gigahertz, 24 GHz) in amillimeter wave frequency band. As defined herein, acoustic millimeterwave means an acoustic wave having a frequency within a range extendingfrom eight Gigahertz (8 GHz) to three hundred Gigahertz (300 GHz).Temperature compensating bulk acoustic wave resonators 2001A through2001I may, but need not be, temperature compensating bulk acoustic SuperHigh Frequency (SHF) wave resonators 2001A through 2001I or temperaturecompensating bulk acoustic Extremely High Frequency (EHF) waveresonators 2001A through 2001I, as the terms Super High Frequency (SHF)and Extremely High Frequency (EHF) are defined by the InternationalTelecommunications Union (ITU). For example, temperature compensatingbulk acoustic wave resonators 2001A through 2001I may be temperaturecompensating bulk acoustic Super High Frequency (SHF) wave resonators2001A through 2001I operable with a main resonance mode having a mainresonant frequency that is a Super High Frequency (SHF) (e.g.,twenty-four Gigahertz, 24 GHz) in a Super High Frequency (SHF) wavefrequency band. Temperature compensating piezoelectric layer thicknessesmay be selected to determine the main resonant frequency of temperaturecompensating bulk acoustic Super High Frequency (SHF) wave resonators2001A through 2001I in the Super High Frequency (SHF) wave band (e.g.,twenty-four Gigahertz, 24 GHz main resonant frequency). Similarly, layerthicknesses of Super High Frequency (SHF) reflector layers (e.g., layerthickness of multilayer metal acoustic SHF wave reflector bottomelectrodes 2013A through 2013I, e.g., layer thickness of multilayermetal acoustic SHF wave reflector top electrodes 2015A through 2015I)may be selected to determine peak acoustic reflectivity of such SHFreflectors at a frequency, e.g., peak reflectivity resonant frequency,within the Super High Frequency (SHF) wave band (e.g., a twenty-fourGigahertz, 24 GHz peak reflectivity resonant frequency). Alternatively,temperature compensating piezoelectric layer bulk acoustic waveresonators 2001A through 2001I may be temperature compensating bulkacoustic Extremely High Frequency (EHF) wave resonators 2001A through2001I operable with a main resonance mode having a main resonantfrequency that is an Extremely High Frequency (EHF) wave band (e.g.,thirty-nine Gigahertz, 39 GHz main resonant frequency) in an ExtremelyHigh Frequency (EHF) wave frequency band. Temperature compensatingpiezoelectric layer thicknesses may be selected to determine the mainresonant frequency of temperature compensating bulk acoustic ExtremelyHigh Frequency (EHF) wave resonators 2001A through 2001I in theExtremely High Frequency (EHF) wave band (e.g., thirty-nine Gigahertz,39 GHz main resonant frequency). Similarly, layer thicknesses ofExtremely High Frequency (EHF) reflector layers (e.g., layer thicknessof multilayer metal acoustic EHF wave reflector bottom electrodes 2013Athrough 2013I, e.g., layer thickness of multilayer metal acoustic EHFwave reflector top electrodes 2015A through 2015I) may be selected todetermine peak acoustic reflectivity of such EHF reflectors at afrequency, e.g., peak reflectivity resonant frequency, within theExtremely High Frequency (EHF) wave band (e.g., a thirty-nine Gigahertz,39 GHz peak reflectivity resonant frequency). The general structures ofthe multilayer metal acoustic reflector top electrode and the multilayermetal acoustic reflector bottom electrode have already been discussedpreviously herein with respect of FIGS. 1A and 1B. As already discussed,these structures are directed to respective pairs of metal electrodelayers, in which a first member of the pair has a relatively lowacoustic impedance (relative to acoustic impedance of an other member ofthe pair), in which the other member of the pair has a relatively highacoustic impedance (relative to acoustic impedance of the first memberof the pair), and in which the respective pairs of metal electrodelayers have layer thicknesses corresponding to one quarter wavelength(e.g., one quarter acoustic wavelength) at a main resonant frequency ofthe resonator. Accordingly, it should be understood that the temperaturecompensating bulk acoustic SHF or EHF wave resonators 2001A, 2001B,2000C shown in FIG. 2A include respective multilayer metal acoustic SHFor EHF wave reflector top electrodes 2015A, 2015B, 2015C and multilayermetal acoustic SHF or EHF wave reflector bottom electrodes 2013A, 2013B,2013C, in which the respective pairs of metal electrode layers havelayer thicknesses corresponding to a quarter wavelength (e.g., onequarter of an acoustic wavelength) at a SHF or EHF wave main resonantfrequency of the respective temperature compensating bulk acoustic SHFor EHF wave resonator 2001A, 2001B, 2001C.

Shown in FIG. 2A is a temperature compensating bulk acoustic SHF or EHFwave resonator 2001A including a normal axis temperature compensatingpiezoelectric layer 201A sandwiched between multilayer metal acousticSHF or EHF wave reflector top electrode 2015A and multilayer metalacoustic SHF or EHF wave reflector bottom electrode 2013A. Also shown inFIG. 2A is a temperature compensating bulk acoustic SHF or EHF waveresonator 2001B including a normal axis temperature compensatingpiezoelectric layer 201B and a reverse axis temperature compensatingpiezoelectric layer 202B arranged in a two piezoelectric layeralternating stack arrangement sandwiched between multilayer metalacoustic SHF or EHF wave reflector top electrode 2015B and multilayermetal acoustic SHF or EHF wave reflector bottom electrode 2013B. Atemperature compensating bulk acoustic SHF or EHF wave resonator 2001Cincludes a normal axis temperature compensating piezoelectric layer201C, a reverse axis temperature compensating piezoelectric layer 202C,and another normal axis temperature compensating piezoelectric layer203C arranged in a three temperature compensating piezoelectric layeralternating stack arrangement sandwiched between multilayer metalacoustic SHF or EHF wave reflector top electrode 2015C and multilayermetal acoustic SHF or EHF wave reflector bottom electrode 2013C.

Included in FIG. 2B is temperature compensating bulk acoustic SHF or EHFwave resonator 2001D in a further simplified view similar to thetemperature compensating bulk acoustic wave resonator structure shown inFIGS. 1A and 1B and including a normal axis piezoelectric layer 201D, areverse axis temperature compensating piezoelectric layer 202D, andanother normal axis temperature compensating piezoelectric layer 203D,and another reverse axis temperature compensating piezoelectric layer204D arranged in a four temperature compensating piezoelectric layeralternating stack arrangement sandwiched between multilayer metalacoustic SHF or EHF wave reflector top electrode 2015D and multilayermetal acoustic SHF or EHF wave reflector bottom electrode 2013D. Atemperature compensating bulk acoustic SHF or EHF wave resonator 2001Eincludes a normal axis temperature compensating piezoelectric layer201E, a reverse axis temperature compensating piezoelectric layer 202E,another normal axis piezoelectric layer 203E, another reverse axistemperature compensating piezoelectric layer 204E, and yet anothernormal axis temperature compensating piezoelectric layer 205E arrangedin a five temperature compensating piezoelectric layer alternating stackarrangement sandwiched between multilayer metal acoustic SHF or EHF wavereflector top electrode 2015E and multilayer metal acoustic SHF or EHFwave reflector bottom electrode 2013E. A temperature compensating bulkacoustic SHF or EHF wave resonator 2001F includes a normal axistemperature compensating piezoelectric layer 201F, a reverse axistemperature compensating piezoelectric layer 202F, another normal axistemperature compensating piezoelectric layer 203F, another reverse axistemperature compensating piezoelectric layer 204F, yet another normalaxis temperature compensating piezoelectric layer 205F, and yet anotherreverse axis temperature compensating piezoelectric layer 206F arrangedin a six temperature compensating piezoelectric layer alternating stackarrangement sandwiched between multilayer metal acoustic SHF or EHF wavereflector top electrode 2015F and multilayer metal acoustic SHF or EHFwave reflector bottom electrode 2013F.

In FIG. 2A, shown directly to the right of the temperature compensatingbulk acoustic SHF or EHF wave resonator 2001A including the normal axispiezoelectric layer 201A, is a corresponding diagram 2019A depicting itsimpedance versus frequency response during its electrical operation, aspredicted by simulation. The diagram 2019A depicts the main resonantpeak 2021A of the main resonant mode of the temperature compensatingbulk acoustic SHF or EHF wave resonator 2001A at its main resonantfrequency (e.g., its 24 GHz series resonant frequency). The diagram2019A also depicts the satellite resonance peaks 2023A of the satelliteresonant modes of the temperature compensating bulk acoustic SHF or EHFwave resonator 2001A at satellite frequencies above and below the mainresonant frequency 2021A (e.g., above and below the 24 GHz seriesresonant frequency). Relatively speaking, the main resonant modecorresponding to the main resonance peak 2021A is the strongest resonantmode because it is stronger than all other resonant modes of theresonator 2001A, (e.g., stronger than the satellite modes correspondingto relatively lesser satellite resonance peaks 2023A).

Similarly, in FIGS. 2A and 2B, shown directly to the right of thetemperature compensating bulk acoustic SHF or EHF wave resonators 2001Bthrough 2001F are respective corresponding diagrams 2019B through 2019Fdepicting corresponding impedance versus frequency response duringelectrical operation, as predicted by simulation. The diagrams 2019Bthrough 2019F depict respective example SHF main resonant peaks 2021Bthrough 2021F of respective corresponding main resonant modes of exampletemperature compensating bulk acoustic SHF wave resonators 2001B through2001F at respective corresponding main resonant frequencies (e.g.,respective 24 GHz series resonant frequencies). The diagrams 2019Bthrough 2019F also depict respective satellite resonance peaks 2023Bthrough 2023F of respective corresponding satellite resonant modes ofthe example temperature compensating bulk acoustic SHF wave resonators2001B through 2001F at respective corresponding satellite frequenciesabove and below the respective corresponding main resonant frequencies2021B through 2021F (e.g., above and below the corresponding respective24 GHz series resonant frequencies). Relatively speaking, for thecorresponding respective main resonant modes, its correspondingrespective main resonance peak 2021B through 2021F is the strongest forits example temperature compensating bulk acoustic SHF wave resonators2001B through 2001F (e.g., stronger than the corresponding respectivesatellite modes and corresponding respective lesser satellite resonancepeaks 2023B). The International Telecommunication Union (ITU) definesthe super high frequency band as extending between three Gigahertz (3GHz) and thirty Gigahertz (30 GHz). The ITU extremely high frequencyband is defined as extending between thirty Gigahertz (30 GHz) and threehundred Gigahertz (300 GHz). The 24 GHz design of the example bulkacoustic SHF wave resonator 2001F having the alternating axis stack ofthe six doped piezoelectric layers is an example of an ITU super highfrequency resonator. It is disclosed herein that proportional scaling oflayer thickness may provide alternative frequency resonators to thedisclosed 24 GHz design, e.g., proportional layer thickness upscalingmay provide 37 GHz and 77 GHz EHF designs. The example scaled 37 GHz and77 GHz designs of the example bulk acoustic EHF wave resonator 2001Fhaving the alternating axis stack of the six doped piezoelectric layersare examples of ITU Extremely High Frequency (EHF) resonators. Asmentioned previously, FIG. 2C shows additional alternative temperaturecompensating bulk acoustic wave resonator structures with additionalnumbers of alternating axis temperature compensating piezoelectriclayers. A temperature compensating bulk acoustic SHF or EHF waveresonator 2001G includes four normal axis temperature compensatingpiezoelectric layers 201G, 203G, 205G, 207G, and four reverse axistemperature compensating piezoelectric layers 202G, 204G, 206G, 208Garranged in an eight temperature compensating piezoelectric layeralternating stack arrangement sandwiched between multilayer metalacoustic SHF or EHF wave reflector top electrode 2015G and multilayermetal acoustic SHF or EHF wave reflector bottom electrode 2013G. Atemperature compensating bulk acoustic SHF or EHF wave resonator 2001Hincludes five normal axis temperature compensating piezoelectric layers201H, 203H, 205H, 207H, 209H and five reverse axis temperaturecompensating piezoelectric layers 202H, 204H, 206H, 208H, 210H arrangedin a ten piezoelectric layer alternating stack arrangement sandwichedbetween multilayer metal acoustic SHF or EHF wave reflector topelectrode 2015H and multilayer metal acoustic SHF or EHF wave reflectorbottom electrode 2013H. A temperature compensating bulk acoustic SHF orEHF wave resonator 2001I includes nine normal axis temperaturecompensating piezoelectric layers 201I, 203I, 205I, 207I, 209I, 211I,213I, 215I, 217I and nine reverse axis temperature compensatingpiezoelectric layers 202I, 204I, 206I, 208I, 210I, 212I, 214I, 216I,218I arranged in an eighteen temperature compensating piezoelectriclayer alternating stack arrangement sandwiched between multilayer metalacoustic SHF or EHF wave reflector top electrode 2015I and multilayermetal acoustic SHF or EHF wave reflector bottom electrode 2013I.

In the example resonators, 2001A through 2001I, of FIGS. 2A through 2C,a notional heavy dashed line is used in depicting respective etched edgeregion, 253A through 253I, associated with the example resonators, 2001Athrough 2001I. Similarly, in the example resonators, 2001A through2001I, of FIGS. 2A through 2C, a laterally opposed etched edge region254A through 254I may be arranged laterally opposite from etched edgeregion, 253A through 253I. The respective etched edge region may, butneed not, assist with acoustic isolation of the resonators, 2001Athrough 2001I. The respective etched edge region may, but need not, helpwith avoiding acoustic losses for the resonators, 2001A through 2001I.The respective etched edge region, 253A through 253I, (and the laterallyopposed etched edge region 254A through 254I) may extend along thethickness dimension of the respective temperature compensatingpiezoelectric layer stack. The respective etched edge region, 253Athrough 253I, (and the laterally opposed etched edge region 254A through254I) may extend through (e.g., entirely through or partially through)the respective temperature compensating piezoelectric layer stack. Therespective etched edge region, 253A through 253I may extend through(e.g., entirely through or partially through) the respective firsttemperature compensating piezoelectric layer, 201A through 201I. Therespective etched edge region, 253B through 253I, (and the laterallyopposed etched edge region 254B through 254I) may extend through (e.g.,entirely through or partially through) the respective second temperaturecompensating piezoelectric layer, 202B through 202I. The respectiveetched edge region, 253C through 253I, (and the laterally opposed etchededge region 254C through 254I) may extend through (e.g., entirelythrough or partially through) the respective third temperaturecompensating piezoelectric layer, 203C through 203I. The respectiveetched edge region, 253D through 253I, (and the laterally opposed etchededge region 254D through 254I) may extend through (e.g., entirelythrough or partially through) the respective fourth temperaturecompensating piezoelectric layer, 204D through 204I. The respectiveetched edge region, 253E through 253I, (and the laterally opposed etchededge region 254E through 254I) may extend through (e.g., entirelythrough or partially through) the respective additional temperaturecompensating piezoelectric layers of the resonators, 2001E through2001I. The respective etched edge region, 253A through 253I, (and thelaterally opposed etched edge region 254A through 254I) may extend alongthe thickness dimension of the respective multilayer metal acoustic SHFor EHF wave reflector bottom electrode, 2013A through 2013I, of theresonators, 2001A through 2001I. The respective etched edge region, 253Athrough 253I, (and the laterally opposed etched edge region 254A through254I) may extend through (e.g., entirely through or partially through)the respective multilayer metal acoustic SHF or EHF wave reflectorbottom electrode, 2013A through 2013I. The respective etched edgeregion, 253A through 253I, (and the laterally opposed etched edge region254A through 254I) may extend along the thickness dimension of therespective multilayer metal acoustic SHF or EHF wave reflector topelectrode, 2015A through 2015I of the resonators, 2001A through 2001I.The etched edge region, 253A through 253I, (and the laterally opposedetched edge region 254A through 254I) may extend through (e.g., entirelythrough or partially through) the respective multilayer metal acousticSHF or EHF wave reflector top electrode, 2015A through 2015I.

As shown in FIGS. 2A through 2C, first mesa structures corresponding tothe respective stacks of piezoelectric material layers may extendlaterally between (e.g., may be formed between) etched edge regions 253Athrough 253I and laterally opposing etched edge region 254A through254I. Second mesa structures corresponding to multilayer metal acousticSHF or EHF wave reflector bottom electrode 2013A through 2013I mayextend laterally between (e.g., may be formed between) etched edgeregions 153A through 153I and laterally opposing etched edge region 154Athrough 154I. Third mesa structures corresponding to multilayer metalacoustic SHF or EHF wave reflector top electrode 2015A through 2015I mayextend laterally between (e.g., may be formed between) etched edgeregions 153A through 153I and laterally opposing etched edge region 154Athrough 154I.

In accordance with the teachings herein, various temperaturecompensating bulk acoustic SHF or EHF wave resonators may include: aseven temperature compensating piezoelectric layer alternating axisstack arrangement; a nine temperature compensating piezoelectric layeralternating axis stack arrangement; an eleven temperature compensatingpiezoelectric layer alternating axis stack arrangement; a twelvetemperature compensating piezoelectric layer alternating axis stackarrangement; a thirteen temperature compensating piezoelectric layeralternating axis stack arrangement; a fourteen temperature compensatingpiezoelectric layer alternating axis stack arrangement; a fifteentemperature compensating piezoelectric layer alternating axis stackarrangement; a sixteen temperature compensating piezoelectric layeralternating axis stack arrangement; and a seventeen temperaturecompensating piezoelectric layer alternating axis stack arrangement; andthat these stack arrangements may be sandwiched between respectivemultilayer metal acoustic SHF or EHF wave reflector top electrodes andrespective multilayer metal acoustic SHF or EHF wave reflector bottomelectrodes. Mass load layers and lateral features (e.g., step features)as discussed previously herein with respect to FIG. 1A are notexplicitly shown in the simplified diagrams of the various resonatorsshown in FIGS. 2A, 2B and 2C. However, such mass load layers may beincluded, and such lateral features may be included, and may be arrangedbetween, for example, top metal electrode layers of the respective topacoustic reflectors of the resonators shown in FIGS. 2A, 2B and 2C.Further, such mass load layers may be included, and such lateralfeatures may be included, and may be arranged between, for example, topmetal electrode layers of the respective top acoustic reflectors in thevarious resonators having the alternating axis stack arrangements ofvarious numbers of temperature compensating piezoelectric layers, asdescribed in this disclosure.

In SHF examples, thicknesses of temperature compensating piezoelectriclayers (e.g., thicknesses of the normal axis temperature compensatingpiezoelectric layer 201A through 201I, e.g., thicknesses of the reverseaxis temperature compensating piezoelectric layer 202A through 202I) maybe selected to determine the main resonant frequency of temperaturecompensating bulk acoustic Super High Frequency (SHF) wave resonator2001A through 2001I in the Super High Frequency (SHF) wave band (e.g.,approximately twenty-four Gigahertz, approximately 24 GHz main resonantfrequency). Similarly, in SHF examples, layer thicknesses of Super HighFrequency (SHF) acoustic reflector electrode layers (e.g., member layerthicknesses of Super High frequency (SHF) bottom acoustic reflectorelectrode 2013A through 2013I, e.g., member layer thickness of SuperHigh frequency (SHF) top acoustic reflector electrode 2015A through2015I) may be selected to determine peak acoustic reflectivity of suchSHF acoustic reflector electrodes at a frequency, e.g., peakreflectivity resonant frequency, within the Super High Frequency (SHF)wave band (e.g., approximately twenty-four Gigahertz, approximately 24GHz peak reflectivity resonant frequency). The Super High Frequency(SHF) wave band may include: 1) peak reflectivity resonant frequency(e.g., approximately twenty-four Gigahertz, approximately 24 GHz peakreflectivity resonant frequency) of the Super High Frequency (SHF)acoustic reflector electrode layers; and 2) the main resonant frequencyof temperature compensating bulk acoustic the Super High Frequency (SHF)wave resonator 2001A through 2001I (e.g., approximately twenty-fourGigahertz, approximately 24 GHz main resonant frequency).

In EHF examples, thicknesses of temperature compensating piezoelectriclayers (e.g., thicknesses of the normal axis temperature compensatingpiezoelectric layer 201A through 201I, e.g., thicknesses of the reverseaxis temperature compensating piezoelectric layer 202A through 202I) maybe selected to determine the main resonant frequency of temperaturecompensating bulk acoustic Extremely High Frequency (EHF) wave resonator2001A through 2001I in the Extremely High Frequency (EHF) wave band(e.g., 39 GHz main resonant frequency, e.g., 77 GHz main resonantfrequency). Similarly, in EHF examples, layer thicknesses of ExtremelyHigh Frequency (EHF) acoustic reflector electrode layers (e.g., memberlayer thicknesses of Super High frequency (SHF) bottom acousticreflector electrode 2013A through 2013I, e.g., member layer thickness ofSuper High frequency (SHF) top acoustic reflector electrode 2015Athrough 2015I) may be selected to determine peak acoustic reflectivityof such EHF acoustic reflector electrodes at a frequency, e.g., peakreflectivity resonant frequency, within the Extremely High Frequency(EHF) wave band (e.g., 39 GHz peak reflectivity resonant frequency,e.g., 77 GHz peak reflectivity resonant frequency). The Extremely HighFrequency (EHF) wave band may include: 1) peak reflectivity resonantfrequency (e.g., 39 GHz peak reflectivity resonant frequency, e.g., 77GHz peak reflectivity resonant frequency) of the Extremely HighFrequency (EHF) acoustic reflector electrode layers; and 2) the mainresonant frequency of temperature compensating bulk acoustic theExtremely High Frequency (EHF) wave resonator 2001A through 2001I (e.g.,39 GHz main resonant frequency, e.g., 77 GHz main resonant frequency).

For example, relatively low acoustic impedance titanium (Ti) metal andrelatively high acoustic impedance Molybdenum (Mo) metal may bealternated for member layers of the bottom acoustic reflector electrode2013A through 2013I, and for member layers of top acoustic reflectorelectrode 2015A through 2015I. Accordingly, these member layers may bedifferent metals from one another having respective acoustic impedancesthat are different from one another so as to provide a reflectiveacoustic impedance mismatch at the resonant frequency of the resonator.For example, a first member may have an acoustic impedance, and a secondmember may have a relatively higher acoustic impedance that is at leastabout twice (e.g., twice) as high as the acoustic impedance of the firstmember.

Thicknesses of member layers of the acoustic reflector electrodes may berelated to resonator resonant frequency. Member layers of the acousticreflector electrodes may be made thinner as resonators are made toextend to higher resonant frequencies, and as acoustic reflectorelectrodes are made to extend to higher peak reflectivity resonantfrequencies. In accordance with teachings of this disclosure, tocompensate for this member layer thinning, number of member layers ofthe acoustic reflector electrodes may be increased in designs extendingto higher resonant frequencies, to facilitate thermal conductivitythrough acoustic reflector electrodes, and to facilitate electricalconductivity through acoustic reflectivity at higher resonantfrequencies. Operation of the example temperature compensating bulkacoustic wave resonators 2001A through 2001I at a resonant Super HighFrequency (SHF) or resonant Extremely High Frequency (EHF) may generateheat to be removed from temperature compensating bulk acoustic waveresonators 2001A through 2001I through the acoustic reflectorelectrodes. The acoustic reflector electrodes (e.g., Super HighFrequency (SHF) bottom acoustic reflector electrode 2013A through 2013I,e.g., Super High Frequency (SHF) top acoustic reflector electrode 2015Athrough 2015I, e.g., Extremely High Frequency (EHF) bottom acousticreflector electrode 2013A through 2013I, e.g., Extremely High Frequency(EHF) top acoustic reflector electrode 2015A through 2015I) may havethermal resistance of three thousand degrees Kelvin per Watt or less atthe given frequency (e.g., at the resonant frequency of the temperaturecompensating BAW resonator in the Super High Frequency (SHF) band or theExtremely High Frequency (EHF) band, e.g., at the peak reflectivityresonant frequency of the acoustic reflector electrode in the Super HighFrequency (SHF) band or the Extremely High Frequency (EHF) band). Forexample, a sufficient number of member layers may be employed to providefor this thermal resistance at the given frequency (e.g., at theresonant frequency of the temperature compensating BAW resonator in theSuper High Frequency (SHF) band or the Extremely High Frequency (EHF)band, e.g., at the peak reflectivity resonant frequency of the acousticreflector electrode in the Super High Frequency (SHF) band or theExtremely High Frequency (EHF) band).

Further, quality factor (Q factor) is a figure of merit for temperaturecompensating bulk acoustic wave resonators that may be related, in part,to acoustic reflector electrode conductivity. In accordance with theteachings of this disclosure, without an offsetting compensation thatincreases number of member layers, member layer thinning with increasingfrequency may otherwise diminish acoustic reflector electrodeconductivity, and may otherwise diminish quality factor (Q factor) oftemperature compensating bulk acoustic wave resonators. In accordancewith the teachings of this disclosure, number of member layers of theacoustic reflector electrodes may be increased in designs extending tohigher resonant frequencies, to facilitate electrical conductivitythrough acoustic reflector electrodes. The acoustic reflector electrodes(e.g., Super High Frequency (SHF) bottom acoustic reflector electrode2013A through 2013I, e.g., Super High Frequency (SHF) top acousticreflector electrode 2015A through 2015I, e.g., Extremely High Frequency(EHF) bottom acoustic reflector electrode 2013A through 2013I, e.g.,Extremely High Frequency (EHF) top acoustic reflector electrode 2015Athrough 2015I) may have sheet resistance of less than one Ohm per squareat the given frequency (e.g., at the resonant frequency of thetemperature compensating BAW resonator in the Super High Frequency bandor the Extremely High Frequency band, e.g., at the peak reflectivityresonant frequency of the acoustic reflector electrode in the Super HighFrequency band or the Extremely High Frequency band). For example, asufficient number of member layers may be employed to provide for thissheet resistance at the given frequency (e.g., at the main resonantfrequency of the temperature compensating BAW resonator in the SuperHigh Frequency band or the Extremely High Frequency band, e.g., at thepeak reflectivity resonant frequency of the acoustic reflector electrodein the Super High Frequency band or the Extremely High Frequency band).This may, but need not, facilitate enhancing quality factor (Q factor)to a quality factor (Q factor) that may be above a desired one thousand(1000).

Further, it should be understood that similar to the example firstinterposer layer 166A as discussed previously herein with respect toFIG. 1A, first interposer layer 266C, 266D, 266E, 266F, 266G, 266H, 266Iis explicitly shown in the simplified diagrams of some exampletemperature compensating bulk acoustic wave resonators 2001C through2001I shown in FIGS. 2A, 2B and 2C. The first interposer layer 266C,266D, 266E, 266F, 266G, 266H, 266I may be included and interposedbetween adjacent temperature compensating piezoelectric layers 202C,203C, through 202I, 203I in the example temperature compensating bulksacoustic wave some resonators 2001C through 2001I shown in FIGS. 2A, 2Band 2C. Further, additional interposer layers may be included andinterposed between adjacent temperature compensating piezoelectriclayers in the various resonators having the alternating axis stackarrangements of various numbers of temperature compensatingpiezoelectric layers, as described in this disclosure. For example,second interposer layer 268E, 268F, 268G, 268H, 268I may be included andinterposed between adjacent fourth and fifth temperature compensatingpiezoelectric layers 204E, 205E, through 204I, 205I in temperaturecompensating bulk acoustic wave some resonators 2001E through 2001Ishown in FIGS. 2B and 2C. For example, third interposer layer 270G,270H, 270I may be included and interposed between adjacent sixth andseventh temperature compensating piezoelectric layers 206G, 207G,through 206I, 207I in temperature compensating bulk acoustic waveresonators 2001G through 2001I shown in FIG. 2C. For example, fourthinterposer layer 272G, 272I may be included and interposed betweenadjacent eighth and ninth temperature compensating piezoelectric layers208G, 209G, 208I, 209I in the temperature compensating bulk acousticwave resonators 2001G and 2001I shown in FIG. 2C. For example, fifthinterposer layer 274I may be included and interposed between adjacenttenth and eleventh temperature compensating piezoelectric layers 210I,211I in the example temperature compensating bulk acoustic waveresonator 2001I shown in FIG. 2C. For example, sixth interposer layer276I may be included and interposed between adjacent twelfth andthirteenth temperature compensating piezoelectric layers 212I, 213I inthe example temperature compensating bulk acoustic wave resonator 2001Ishown in FIG. 2C. For example, seventh interposer layer 278I may beincluded and interposed between adjacent temperature compensatingpiezoelectric layers 214I, 215I in the example temperature compensatingbulk acoustic wave resonator 2001I shown in FIG. 2C. For example, eighthinterposer layer 280I may be included and interposed between adjacentsixteenth and seventeenth temperature compensating piezoelectric layers216I, 217I in the example temperature compensating bulk acoustic waveresonator 2001I shown in FIG. 2C.

Further, in some other alternative temperature compensating bulkacoustic wave resonator structures, other interposer layers may beemployed. FIG. 2D shows a temperature compensating bulk acoustic waveresonator structure 2001J, similar to temperature compensating bulkacoustic wave resonator structure 2001F shown in FIG. 2B, but in moredetailed view. The temperature compensating bulk acoustic wave resonatorstructure 2001J includes six temperature compensating piezoelectriclayers 201J through 206J each having respective piezoelectric axis. Thesix layers of the first temperature compensating piezoelectric layer201J through sixth temperature compensating piezoelectric layer 206J arearranged in an alternating piezoelectric axis stack arrangement. Thesesix layers 201J through 206J are sandwiched between multilayer metalacoustic SHF or EHF wave reflector bottom electrode 213J and multilayermetal acoustic SHF or EHF wave reflector top electrode 215J. The firsttemperature compensating piezoelectric layer 201J comprises a first pairof sublayers of piezoelectric material 201JA, 201JB, and a first layerof temperature compensating material 259J (e.g., comprising SiliconDioxide (SiO₂) layer, e.g., comprising metal sublayer over SiliconDioxide (SiO₂) sublayer) interposed between first and second members ofthe first pair of sublayers of piezoelectric material 201JA, 201JB. Thesecond temperature compensating piezoelectric layer 202J comprises asecond pair of sublayers of piezoelectric material 202JA, 202JB, and asecond layer of temperature compensating material 261J (e.g., comprisingSilicon Dioxide (SiO₂) layer, e.g., comprising metal sublayer overSilicon Dioxide (SiO₂) sublayer) interposed between first and secondmembers of the second pair of sublayers of piezoelectric material 202JA,202JB. The third temperature compensating piezoelectric layer 203Jcomprises a third pair of sublayers of piezoelectric material 203JA,203JB, and a third layer of temperature compensating material 263JJ(e.g., comprising Silicon Dioxide (SiO₂) layer, e.g., comprising metalsublayer over Silicon Dioxide (SiO₂) sublayer) interposed between firstand second members of the third pair of sublayers of piezoelectricmaterial 203JA, 203JB. The fourth temperature compensating piezoelectriclayer 204J comprises a fourth pair of sublayers of piezoelectricmaterial 204JA, 204JB, and a fourth layer of temperature compensatingmaterial 264J (e.g., comprising Silicon Dioxide (SiO₂) layer, e.g.,comprising metal sublayer over Silicon Dioxide (SiO₂) sublayer)interposed between first and second members of the fourth pair ofsublayers of piezoelectric material 204JA, 204JB. The fifth temperaturecompensating piezoelectric layer 205J comprises a fifth pair ofsublayers of piezoelectric material 205JA, 205JB, and a fifth layer oftemperature compensating material 265J (e.g., comprising Silicon Dioxide(SiO₂) layer, e.g., comprising metal sublayer over Silicon Dioxide(SiO₂) sublayer) interposed between first and second members of thefifth pair of sublayers of piezoelectric material 205JA, 205JB. Thesixth temperature compensating piezoelectric layer 206J comprises asixth pair of sublayers of piezoelectric material 206JA, 206JB, and asixth layer of temperature compensating material 267J (e.g., comprisingSilicon Dioxide (SiO₂) layer, e.g., comprising metal sublayer overSilicon Dioxide (SiO₂) sublayer) interposed between first and secondmembers of the sixth pair of sublayers of piezoelectric material 206JA,206JB. For example, FIG. 2D shows a first interposer layer 266J (e.g.,comprising first dielectric interposer layer 266J, e.g., comprisingfirst metal interposer layer 266J, e.g., comprising first metalinterposer sublayer over first dielectric interposer sublayer)interposed between second layer of (reverse axis) temperaturecompensating piezoelectric material 202J and third layer of (normalaxis) temperature compensating piezoelectric material 203J.

As shown in FIG. 2D in a first detailed view 220J, a top member 201JB ofthe first pair of sublayers of the first temperature compensatingpiezoelectric layer together with a bottom member 202JA of the secondtemperature compensating piezoelectric layer may be a monolithic layer222J of piezoelectric material (e.g., Aluminum Nitride (AlN)) havingfirst and second regions 224J, 226J. A central region of monolithiclayer 222J of piezoelectric material (e.g., Aluminum Nitride (AlN))between first and second regions 224J, 226J may be oxygen rich. Thefirst region 224J of monolithic layer 222J (e.g., bottom region 224J ofmonolithic layer 222J) has a first piezoelectric axis orientation (e.g.,normal axis orientation) as representatively illustrated in detailedview 220J using a downward pointing arrow at first region 224J, (e.g.,bottom region 224J). This first piezoelectric axis orientation (e.g.,normal axis orientation, e.g., downward pointing arrow) at first region224J of monolithic layer 222J (e.g., bottom region 224J of monolithiclayer 222J) corresponds to the first piezoelectric axis orientation(e.g., normal axis orientation, e.g., downward pointing arrow) of thetop member 201JB of the first pair of sublayers of the first temperaturecompensating piezoelectric layer. The second region 226J of monolithiclayer 222J (e.g., top region 226J of monolithic layer 222J) has a secondpiezoelectric axis orientation (e.g., reverse axis orientation) asrepresentatively illustrated in detailed view 220J using an upwardpointing arrow at second region 226J, (e.g., top region 226J). Thissecond piezoelectric axis orientation (e.g., reverse axis orientation,e.g., upward pointing arrow) at second region 226J of monolithic layer222J (e.g., top region 226J of monolithic layer 222J) may be formed tooppose the first piezoelectric axis orientation (e.g., normal axisorientation, e.g., downward pointing arrow) at first region 224J ofmonolithic layer 222J (e.g., bottom region 224J of monolithic layer222J) by adding gas (e.g., oxygen) to flip the axis while sputtering thesecond region 226J of monolithic layer 222J (e.g., top region 226J ofmonolithic layer 222J) onto the first region 224J of monolithic layer222J (e.g., bottom region 224J of monolithic layer 222J). The secondpiezoelectric axis orientation (e.g., reverse axis orientation, e.g.,upward pointing arrow) at second region 226J of monolithic layer 222J(e.g., top region 226J of monolithic layer 222J) corresponds to thesecond piezoelectric axis orientation (e.g., reverse axis orientation,e.g., upward pointing arrow) of bottom member 202JA of the secondtemperature compensating piezoelectric layer.

Similarly, as shown in FIG. 2D in a second detailed view 230J, a topmember 203JB of the first pair of sublayers of the third temperaturecompensating piezoelectric layer together with a bottom member 204JA ofthe fourth temperature compensating piezoelectric layer may be anadditional monolithic layer 232J of piezoelectric material (e.g.,Aluminum Nitride (AlN)) having first and second regions 234J, 236J. Acentral region of additional monolithic layer 232J of temperaturecompensating piezoelectric material (e.g., Aluminum Nitride (AlN))between first and second regions 234J, 236J may be oxygen rich. Thefirst region 234J of additional monolithic layer 232J (e.g., bottomregion 234J of additional monolithic layer 232J) has the firstpiezoelectric axis orientation (e.g., normal axis orientation) asrepresentatively illustrated in second detailed view 230J using thedownward pointing arrow at first region 234J, (e.g., bottom region224J). This first piezoelectric axis orientation (e.g., normal axisorientation, e.g., downward pointing arrow) at first region 234J ofadditional monolithic layer 232J (e.g., bottom region 234J of additionalmonolithic layer 232J) corresponds to the first piezoelectric axisorientation (e.g., normal axis orientation, e.g., downward pointingarrow) of the top member 203JB of the third pair of sublayers of thethird temperature compensating piezoelectric layer. The second region236J of additional monolithic layer 232J (e.g., top region 236J ofadditional monolithic layer 232J) has the second piezoelectric axisorientation (e.g., reverse axis orientation) as representativelyillustrated in second detailed view 230J using the upward pointing arrowat second region 236J, (e.g., top region 236J). This secondpiezoelectric axis orientation (e.g., reverse axis orientation, e.g.,upward pointing arrow) at second region 236J of additional monolithiclayer 232J (e.g., top region 236J of additional monolithic layer 232J)may be formed to oppose the first piezoelectric axis orientation (e.g.,normal axis orientation, e.g., downward pointing arrow) at first region234J of additional monolithic layer 232J (e.g., bottom region 234J ofadditional monolithic layer 232J) by adding gas (e.g., oxygen) to flipthe axis while sputtering the second region 236J of additionalmonolithic layer 232J (e.g., top region 236J of additional monolithiclayer 232J) onto the first region 234J of additional monolithic layer232J (e.g., bottom region 234J of additional monolithic layer 232J). Thesecond piezoelectric axis orientation (e.g., reverse axis orientation,e.g., upward pointing arrow) at second region 236J of additionalmonolithic layer 232J (e.g., top region 236J of additional monolithiclayer 232J) corresponds to the second piezoelectric axis orientation(e.g., reverse axis orientation, e.g., upward pointing arrow) of thebottom member 204JA of the fourth pair of sublayers of the fourthtemperature compensating piezoelectric layer.

For example, FIG. 2D shows a second interposer layer 268J (e.g., seconddielectric interposer layer 268J, e.g., second metal interposer layer268J, e.g., comprising second metal interposer sublayer over seconddielectric interposer sublayer) interposed between fourth layer of(reverse axis) temperature compensating piezoelectric material 204J andfifth layer of (normal axis) temperature compensating piezoelectricmaterial 205J. Similar to what was just discussed, a top member 205JB ofthe fifth pair of sublayers of the fifth temperature compensatingpiezoelectric layer together with a bottom member 206JA of the sixthtemperature compensating piezoelectric layer may be another additionalmonolithic layer of piezoelectric material (e.g., Aluminum Nitride(AlN)) having first and second regions.

Etched edge region 253J (and laterally opposing etched edge region 254J)may extend through (e.g., entirely through, e.g., partially through) thesix temperature compensating piezoelectric layer alternating axis stackarrangement and its interposer layers, and may extend through (e.g.,entirely through, e.g., partially through) multilayer metal acoustic SHFor EHF wave reflector top electrode 2015J, and may extend through (e.g.,entirely through, e.g., partially through) multilayer metal acoustic SHFor EHF wave reflector bottom electrode 2013J. As shown in FIG. 2D, afirst mesa structure corresponding to the stack of six temperaturecompensating piezoelectric material layers 201J through 206J may extendlaterally between (e.g., may be formed between) etched edge region 253Jand laterally opposing etched edge region 254J. A second mesa structurecorresponding to multilayer metal acoustic SHF or EHF wave reflectorbottom electrode 2013J may extend laterally between (e.g., may be formedbetween) etched edge region 153J and laterally opposing etched edgeregion 154J. Third mesa structure corresponding to multilayer metalacoustic SHF or EHF wave reflector top electrode 2015J may extendlaterally between (e.g., may be formed between) etched edge region 153Jand laterally opposing etched edge region 154J.

One or more (e.g., one or a plurality of) layers of temperaturecompensating material may comprise metal and dielectric for respectivelayers of temperature compensating material. For example, in FIG. 2D oneor more of the layers of temperature compensating material (e.g.,temperature compensating layer 267J) may comprise metal and dielectricfor respective interposer layers. For example, detailed view 240J oftemperature compensating layer 267J shows temperature compensating layer267J as comprising metal sublayer 267JB over dielectric (e.g., silicondioxide) sublayer 267JA. For temperature compensating layer 267J,example thickness of metal sublayer 267JB may be approximately twohundred Angstroms (200 A). For temperature compensating layer 267J,example thickness of dielectric (e.g., silicon dioxide) sublayer 267JAmay be approximately two hundred Angstroms (200 A). The secondpiezoelectric axis orientation (e.g., reverse axis orientation, e.g.,upward pointing arrow) at region 244J (e.g., bottom region 244J)corresponds to the second piezoelectric axis orientation (e.g., reverseaxis orientation, e.g., upward pointing arrow) of first sublayer 206JAof sixth piezoelectric layer 206J. Similarly, the second piezoelectricaxis orientation (e.g., reverse axis orientation, e.g., upward pointingarrow) at region 246J (e.g., top region 246J) corresponds to the secondpiezoelectric axis orientation (e.g., reverse orientation, e.g., upwardpointing arrow) second sublayer 206JB of sixth piezoelectric layer 209J.

As discussed, interposer layers shown in FIG. 1A, and as explicitlyshown in the simplified diagrams of the various resonators shown inFIGS. 2A, 2B, 2C and 2D may be included and interposed between adjacenttemperature compensating piezoelectric layers in the various resonators.Such interposer layers may laterally extend within the mesa structure ofthe stack of temperature compensating piezoelectric layers a fulllateral extent of the stack, e.g., between the etched edge region of thestack and the opposing etched edge region of the stack. However, in someother alternative temperature compensating bulk acoustic wave resonatorstructures, interposer layers may be patterned during fabrication of theinterposer layers (e.g., patterned using masking and selective etchingtechniques during fabrication of the interposer layers). Such patternedinterposer layers need not extend a full lateral extent of the stack(e.g., need not laterally extend to any etched edge regions of thestack.) For example, FIG. 2E shows another alternative temperaturecompensating bulk acoustic wave resonator structure 2001K, similar totemperature compensating bulk acoustic wave resonator structure 2001Jshown in FIG. 2D, but with differences. For example, in the alternativetemperature compensating bulk acoustic wave resonator structure 2001Kshown in FIG. 2E, patterned interposer layers (e.g., first patternedinterposer layer 261K) may be interposed between sequential pairs ofopposing axis temperature compensating piezoelectric layers (e.g., firstpatterned interposer layer 295K may be interposed between a first pairof opposing axis temperature compensating piezoelectric layers 201K,202K, and a second pair of opposing axis temperature compensatingpiezoelectric layers 203K, 204K).

FIG. 2E shows a six temperature compensating piezoelectric layer (201Kthrough 206K) alternating axis stack arrangement having an active regionof the temperature compensating bulk acoustic wave resonator structure2001K sandwiched between overlap of multilayer metal acoustic SHF or EHFwave reflector top electrode 2015IK and multilayer metal acoustic SHF orEHF wave reflector bottom electrode 2013K. In FIG. 2E, patternedinterposer layers (e.g., first patterned interposer layer 266K) may bepatterned to have extent limited to the active region of the temperaturecompensating bulk acoustic wave resonator structure 2001K sandwichedbetween overlap of multilayer metal acoustic SHF or EHF wave reflectortop electrode 2015K and multilayer metal acoustic SHF or EHF wavereflector bottom electrode 2013K. A planarization layer 256K at alimited extent of multilayer metal acoustic SHF or EHF wave reflectorbottom electrode 2013K may facilitate fabrication of the six temperaturecompensating piezoelectric layer alternating axis stack arrangement(e.g., stack of six temperature compensating piezoelectric layers 201Kthrough 201K).

Patterning of interposer layers may be done in various combinations. Forexample, some interposer layers need not be patterned (e.g., may beunpatterned) within lateral extent of the stack of temperaturecompensating piezoelectric layers (e.g., some interposer layers mayextend to full lateral extent of the stack of temperature compensatingpiezoelectric layers). For example, first interposer layer 266J shown inFIG. 2D need not be patterned (e.g., may be unpatterned) within lateralextent of the stack of temperature compensating piezoelectric layers(e.g., first interposer layer 266J may extend to full lateral extent ofthe stack of temperature compensating piezoelectric layers). For examplein FIG. 2D, first interposer layer 266J interposed between firstsequential pair of normal axis and reverse axis temperature compensatingpiezoelectric layers 201J, 202J and adjacent second sequential pair ofnormal axis and reverse axis temperature compensating piezoelectriclayers 203J, 204J need not be patterned within lateral extent of thestack of temperature compensating piezoelectric layers (e.g., firstinterposer layer 266J may extend to full lateral extent of the stack oftemperature compensating piezoelectric layers). In contrast to thisunpatterned interposer layer (e.g., in contrast to unpatternedinterposer layer 266J) as shown in FIG. 2D, in FIG. 2E patternedinterposer layers (e.g., first patterned interposer layer 266K) may bepatterned, for example, to have extent limited to the active region ofthe temperature compensating bulk acoustic wave resonator structure2001K shown in FIG. 2E. First patterned interposer layer 266K may be afirst patterned dielectric interposer layer 266K or a first patternedmetal interposer layer, consistent with interposer layer teachingsdiscussed previously herein. Similarly, in contrast to unpatternedinterposer layer 267J as shown in FIG. 2D, in FIG. 2E second patternedinterposer layer 268K may be patterned, for example, to have extentlimited to the active region of the temperature compensating bulkacoustic wave resonator structure 2001K shown in FIG. 2E. Secondpatterned interposer layer 268K may be a second patterned dielectricinterposer layer 268K or a second patterned metal interposer layer,consistent with interposer layer teachings discussed previously herein.

FIG. 2F shows a comparison of two example bulk acoustic wave resonatorstructures 2001L, 2001M. A first bulk acoustic wave resonator structure2001L shown in FIG. 2F is a first temperature compensating bulk acousticwave resonator 2001L including an alternating axis arrangement of fourtemperature compensating piezoelectric layers 201L, 202L, 203L, 204Lsandwiched between multilayer metal acoustic SHF or EHF wave reflectortop electrodes 2015L and multilayer metal acoustic SHF or EHF wavereflector bottom electrodes 2013L. The first temperature compensatingbulk acoustic wave resonator 2001L may include a first interposer layer266L interposed between the second reverse axis temperature compensatingpiezoelectric layer 202L and the third normal axis temperaturecompensating piezoelectric layer 203L. In accordance with previousdetailed teachings herein, the four temperature compensatingpiezoelectric layers 201L, 202L, 203L, 204L may have respectivethicknesses of about one half wavelength (e.g., one half acousticwavelength) of the main resonant frequency of the first temperaturecompensating bulk acoustic wave resonator 2001L. The first temperaturecompensating bulk acoustic wave resonator 2001L shown in FIG. 2F issimilar to temperature compensating bulk acoustic wave resonator 2001Dshown in FIG. 2B.

For purposes of comparison with the first temperature compensating bulkacoustic wave resonator 2001L shown in FIG. 2F, also shown in FIG. 2F isa second bulk acoustic wave resonator 2001M. The second bulk acousticwave resonator 2001M may include an alternating axis arrangement of fourhalf wavelength thickness piezoelectric layers 201M, 202M, 203M, 204Mwithout temperature compensating material between sublayers of halfwavelength thickness piezoelectric layers 201M, 202M, 203M, 204M. Thefour piezoelectric layers 201M, 202M, 203M, 204M may be sandwichedbetween multilayer metal acoustic SHF or EHF wave reflector topelectrodes 2015M and multilayer metal acoustic SHF or EHF wave reflectorbottom electrodes 2013M. The second bulk acoustic wave resonator 2001Mmay include a first interposer layer 266M interposed at what may be anacoustic energy interaction null between the second reverse axispiezoelectric layer 202M and the third normal axis piezoelectric layer203M. The four piezoelectric layers 201L, 202L, 203L, 204L may haverespective thicknesses of about one half wavelength (e.g., one halfacoustic wavelength) of the main resonant frequency of the second bulkacoustic wave resonator 2001M. For reasons already discussed in detailrelative to FIG. 1B for similarly arranged interposer 166, by similarreasoning, it is likewise theorized that in cases where interposer 266Mmay include temperature compensating material (e.g., Silicon Dioxide(SiO₂)), its arrangement at what may be an acoustic energy interactionnull between the half wavelength thick second reverse axis piezoelectriclayer 202M and the half wavelength thick third normal axis piezoelectriclayer 203M may result in relatively less temperature compensating effect(e.g., relatively less temperature compensating effect than therelatively greater temperature compensating effect of temperaturecompensating piezoelectric layers 201L through 204L.

For purposes of comparison relative to piezoelectric layers 201M, 202M,203M 204M, it is theorized that temperature compensating material intemperature compensated piezoelectric layers 201L, 202L, 203L, 204L mayhave two effects: (a) relative desirable lowering of frequencysensitivity to temperature and (b) relative lowering ofelectromechanical coupling coefficient (Kt2). It is theorized that botheffects may result from acoustic energy being confined in relatively lowacoustic impedance temperature compensating material (e.g., SiliconDioxide temperature compensating material may have a low acousticimpedance relative to MN piezoelectric material).

The foregoing theorizations may be supported by simulations asillustrated in two comparison diagrams 2019N, 2019O shown in FIG. 2F. Afirst diagram 2019N shows temperature coefficient (TC) of frequencychange with temperature in parts per million per degree Celcius (ppm/°C.) versus number of half wavelength thickness alternating axispiezoelectric layers, with examples extending from one half wavelengththickness piezoelectric layer to six half wavelength thicknessalternating axis piezoelectric layers. In diagram 2019N, a solid line2021N shows temperature coefficient (TC) of frequency change withtemperature for half wavelength thickness alternating axis temperaturecompensating piezoelectric layers, with examples extending from one halfwavelength thickness temperature compensating piezoelectric layer to sixhalf wavelength thickness alternating axis temperature compensatingpiezoelectric layers. It is theorized that there may be a positivesynergy between number of half wavelength thickness temperaturecompensating piezoelectric layers and temperature compensating effect. Apossible explanation of this this positive synergy may relate to a moregeneral observation that acoustic velocity in metals may have a strongerdependence on temperature than in piezoelectric layers. Further,resonators with a relatively larger number of half wavelengthpiezoelectric layers may have a relatively larger fraction of acousticenergy confined in piezoelectric layers than in the relatively highertemperature dependent and acoustic velocity sensitive metal electrodes.Accordingly, an undesired resonator frequency drift with increasingtemperature may be reduced for resonators with relatively larger numberof half wavelength piezoelectric layers. Such resonators may exhibitrelatively less temperature sensitivity and relatively less astemperature dependent frequency drift in comparison to resonators with arelatively fewer number of half wavelength piezoelectric layers. Forexample, while solid line 2021N in diagram 2019N shows desirabletemperature compensating for four half wavelength thickness alternatingaxis temperature compensating piezoelectric layers, solid line 2021N indiagram 2019N shows relatively even more desirable temperaturecompensating effect for six half wavelength thickness alternating axistemperature compensating piezoelectric layers (e.g., almost fulltemperature compensating effect at zero ppm/° C.) For sake of comparisonin diagram 2019N, a dashed line 2023N shows temperature coefficient (TC)of frequency change with temperature for half wavelength thicknessalternating axis piezoelectric layers (e.g., without temperaturecompensating material interposing between sublayers of the halfwavelength thickness alternating axis piezoelectric layers), withexamples extending from one half wavelength thickness piezoelectriclayer to six half wavelength thickness alternating axis piezoelectriclayers. Dashed line 2023N in diagram 2019N shows relatively lessdesirable temperature coefficient (TC) of frequency change withtemperature for half wavelength thickness alternating axis piezoelectriclayers (e.g., without temperature compensating material interposingbetween sublayers of the half wavelength thickness alternating axispiezoelectric layers), in comparison to solid line 2021N in diagram2019N, showing desirable temperature compensating effect for halfwavelength thickness alternating axis temperature compensatingpiezoelectric layers.

A second diagram 2019O shows electromechanical coupling coefficient(Kt2) versus number of half wavelength thickness alternating axispiezoelectric layers, with examples extending from one half wavelengththickness piezoelectric layer to six half wavelength thicknessalternating axis piezoelectric layers. In diagram 2019O, a solid line2021O shows electromechanical coupling coefficient (Kt2) for halfwavelength thickness alternating axis temperature compensatingpiezoelectric layers, with examples extending from one half wavelengththickness temperature compensating piezoelectric layer to six halfwavelength thickness alternating axis temperature compensatingpiezoelectric layers. Dashed line 2023O in diagram 2019O showsrelatively higher electromechanical coupling coefficient (Kt2) for halfwavelength thickness alternating axis piezoelectric layers (e.g.,without temperature compensating material interposing between sublayersof the half wavelength thickness alternating axis piezoelectric layers),in comparison to solid line 2021O in diagram 2019O, showing relativelylower electromechanical coupling coefficient (Kt2) for half wavelengththickness alternating axis temperature compensated piezoelectric layers.As discussed, resonators with relatively larger number of halfwavelength piezoelectric layers may have a relatively larger fraction ofacoustic energy confined in piezoelectric layers. Accordingly, theresonators with relatively larger number of half wavelengthpiezoelectric layers may exhibit relatively higher electromechanicalcoupling coefficient (Kt2) as compared to resonators with relativelysmaller number of half wavelength piezoelectric layers. Moreover, sincetemperature compensating material (e.g., Silicon Dioxide temperaturecompensating material) may confine significant portion of acousticenergy in order to achieve the desired temperature compensating effectof frequency response, the electromechanical coupling coefficient (Kt2)may be relatively smaller for temperature compensating resonators(depicted with solid line 2021O in diagram 2019O) as compared toresonators without temperature compensating material (depicted withdashed line 2021O in diagram 2019O).

FIGS. 3A through 3E illustrate example integrated circuit structuresused to form the example temperature compensating bulk acoustic waveresonator structure of FIG. 1A. As shown in FIG. 3A, magnetronsputtering may sequentially deposit layers on silicon substrate 101.Initially, a seed layer 103 of suitable material (e.g., aluminum nitride(AlN), e.g., silicon dioxide (SiO₂), e.g., aluminum oxide (Al₂O₃), e.g.,silicon nitride (Si₃N₄), e.g., amorphous silicon (a-Si), e.g., siliconcarbide (SiC)) may be deposited, for example, by sputtering from arespective target (e.g., from an aluminum, silicon, or silicon carbidetarget). The seed layer may have a layer thickness in a range fromapproximately one hundred Angstroms (100 A) to approximately one micron(1 um). Next, successive pairs of alternating layers of high acousticimpedance metal and low acoustic impedance metal may be deposited byalternating sputtering from targets of high acoustic impedance metal andlow acoustic impedance metal. For example, sputtering targets of highacoustic impedance metal such as Molybdenum or Tungsten may be used forsputtering the high acoustic impedance metal layers, and sputteringtargets of low acoustic impedance metal such as Aluminum or Titanium maybe used for sputtering the low acoustic impedance metal layers. Forexample, the fourth pair of bottom metal electrode layers, 133, 131, maybe deposited by sputtering the high acoustic impedance metal for a firstbottom metal electrode layer 133 of the pair on the seed layer 103, andthen sputtering the low acoustic impedance metal for a second bottommetal electrode layer 131 of the pair on the first layer 133 of thepair. Similarly, the third pair of bottom metal electrode layers, 129,127, may then be deposited by sequentially sputtering from the highacoustic impedance metal target and the low acoustic impedance metaltarget. Similarly, the second pair of bottom metal electrodes 125, 123,may then be deposited by sequentially sputtering from the high acousticimpedance metal target and the low acoustic impedance metal target.Similarly, the first pair of bottom metal electrodes 121, 119, may thenbe deposited by sequentially sputtering from the high acoustic impedancemetal target and the low acoustic impedance metal target. Respectivelayer thicknesses of bottom metal electrode layers of the first, second,third and fourth pairs 119, 121, 123, 125, 127, 129, 131, 133 maycorrespond to approximately a quarter wavelength (e.g., a quarter of anacoustic wavelength) of the resonant frequency at the resonator (e.g.,respective layer thickness of about six hundred Angstroms (660 A) forthe example 24 GHz resonator.) Initial bottom electrode layer 119 maythen be deposited by sputtering from the high acoustic impedance metaltarget. Thickness of the initial bottom electrode layer may be, forexample, about an eighth wavelength (e.g., an eighth of an acousticwavelength) of the resonant frequency of the resonator (e.g., layerthickness of about three hundred Angstroms (300 A) for the example 24GHz resonator.)

A stack of four layers of temperature compensating piezoelectricmaterial, for example, four layers including Aluminum Nitride (AlN)having the wurtzite structure and including temperature compensatingmaterial layer (e.g., Silicon Dioxide layer) may be deposited bysputtering. For example, bottom temperature compensating piezoelectriclayer 105, first middle temperature compensating piezoelectric layer107, second middle temperature compensating piezoelectric layer 109, andtop temperature compensating piezoelectric layer 111 may be deposited bysputtering. The four layers of temperature compensating piezoelectricmaterial in the stack 104, may have the alternating axis arrangement inthe respective stack 104. For example the bottom temperaturecompensating piezoelectric layer 105 may be sputter deposited to havethe normal axis orientation, which is depicted in FIG. 3A using thedownward directed arrow. The first middle temperature compensatingpiezoelectric layer 107 may be sputter deposited to have the reverseaxis orientation, which is depicted in the FIG. 3A using the upwarddirected arrow. The second middle temperature compensating piezoelectriclayer 109 may have the normal axis orientation, which is depicted in theFIG. 3A using the downward directed arrow. The top temperaturecompensating piezoelectric layer may have the reverse axis orientation,which is depicted in the FIG. 3A using the upward directed arrow. Asmentioned previously herein, polycrystalline thin film AlN may be grownin the crystallographic c-axis negative polarization, or normal axisorientation perpendicular relative to the substrate surface usingreactive magnetron sputtering of the Aluminum target in the nitrogenatmosphere. As was discussed in greater detail previously herein,changing sputtering conditions, for example by adding oxygen, mayreverse the axis to a crystallographic c-axis positive polarization, orreverse axis, orientation perpendicular relative to the substratesurface. Sputtering the normal axis bottom temperature compensatingpiezoelectric layer 105 may comprise sputtering a first temperaturecompensating layer 259 (e.g., comprising Silicon Dioxide (SiO₂) layer,e.g., comprising metal sublayer over Silicon Dioxide (SiO₂) sublayer)interposed between sequentially sputtering first and second members ofthe first pair of sublayers of normal axis piezoelectric material (e.g.,AlN) 105A, 105B. Sputtering the reverse axis first middle temperaturecompensating piezoelectric layer 107 may comprise sputtering the secondtemperature compensating layer 161 (e.g., comprising Silicon Dioxide(SiO₂) layer, e.g., comprising metal sublayer over Silicon Dioxide(SiO₂) sublayer) interposed between sequentially sputtering first andsecond members of the second pair of sublayers of reverse axispiezoelectric material (e.g., AlN) 107A, 107B. Sputtering the normalaxis second middle temperature compensating piezoelectric layer 109 maycomprise sputtering the third temperature compensating layer 163 (e.g.,comprising Silicon Dioxide (SiO₂) layer, e.g., comprising metal sublayerover Silicon Dioxide (SiO₂) sublayer) interposed between sequentiallysputtering first and second members of the third pair of sublayers ofnormal axis piezoelectric material (e.g., AlN) 109A, 109B. Sputteringthe reverse axis top temperature compensating piezoelectric layer 111may comprise sputtering the fourth temperature compensating layer 164(e.g., comprising Silicon Dioxide (SiO₂) layer, e.g., comprising metalsublayer over Silicon Dioxide (SiO₂) sublayer) interposed betweensequentially sputtering first and second members of the fourth pair ofsublayers of reverse axis piezoelectric material (e.g., AlN) 111A, 111B.For sputtering of layers of temperature compensating material, thicknessof layers of temperature compensating material may be as alreadydiscussed previously herein.

Interposer layers may be sputtered between sputtering of temperaturecompensating piezoelectric layers, so as to be sandwiched betweentemperature compensating piezoelectric layers of the stack. For example,first interposer layer 166 may be sputtered between sputtering firstmiddle temperature compensating piezoelectric layer 107 and the secondmiddle temperature compensating piezoelectric layer 109 so as to besandwiched between the first middle temperature compensatingpiezoelectric layer 107, and the second middle temperature compensatingpiezoelectric layer 109.

As discussed previously, the first interposer layer 166 may be a metalinterposer layer 166, e.g., high acoustic impedance metal interposerlayer, e.g., Molybdenum metal interposer layer. This may be deposited bysputtering from a metal target. As discussed previously, the firstinterposer layer 166 may be a dielectric interposer layer 166, e.g.,silicon dioxide interposer layer 166. This may be deposited by reactivesputtering from a Silicon target in an oxygen atmosphere. Initialsputter deposition of first interposer layer 166 on reverse axis firstmiddle temperature compensating piezoelectric layer 107 may facilitatesubsequent sputter deposition of normal axis second middle temperaturecompensating piezoelectric layer 109. Sputtering thickness of firstinterposer layer 166 may be as discussed previously herein.

Initial top electrode layer 135 may be deposited on the top temperaturecompensating piezoelectric layer 111 by sputtering from the highacoustic impedance metal target. Thickness of the initial top electrodelayer may be, for example, about an eighth wavelength (e.g., an eighthof an acoustic wavelength) of the resonant frequency of the resonator(e.g., layer thickness of about three hundred Angstroms (300 A) for theexample 24 GHz resonator.) The first pair of top metal electrode layers,137, 139, may then be deposited by sputtering the low acoustic impedancemetal for a first top metal electrode layer 137 of the pair, and thensputtering the high acoustic impedance metal for a second top metalelectrode layer 139 of the pair on the first layer 137 of the pair.Layer thicknesses of top metal electrode layers of the first pair 137,139 may correspond to approximately a quarter wavelength (e.g., aquarter acoustic wavelength) of the resonant frequency of the resonator(e.g., respective layer thickness of about six hundred Angstroms (600 A)for the example 24 GHz resonator.) The optional mass load layer 155 maybe sputtered from a high acoustic impedance metal target onto the secondtop metal electrode layer 139 of the pair. Thickness of the optionalmass load layer may be as discussed previously herein. The mass loadlayer 155 may be an additional mass layer to increase electrode layermass, so as to facilitate the preselected frequency compensation down infrequency (e.g., compensate to decrease resonant frequency).Alternatively, the mass load layer 155 may be a mass load reductionlayer, e.g., ion milled mass load reduction layer 155, to decreaseelectrode layer mass, so as to facilitate the preselected frequencycompensation up in frequency (e.g., compensate to increase resonantfrequency). Accordingly, in such case, in FIG. 3A mass load reductionlayer 155 may representatively illustrate, for example, an ion milledregion of the second member 139 of the first pair of electrodes 137, 139(e.g., ion milled region of high acoustic impedance metal electrode139).

The plurality of lateral features 157 (e.g., patterned layer 157) may beformed by sputtering a layer of additional mass loading having a layerthickness as discussed previously herein. The plurality of lateralfeatures 157 (e.g., patterned layer 157) may be made by patterning thelayer of additional mass loading after it is deposited by sputtering.The patterning may done by photolithographic masking, layer etching, andmask removal. Initial sputtering may be sputtering of a metal layer ofadditional mass loading from a metal target (e.g., a target of Tungsten(W), Molybdenum (Mo), Titanium (Ti) or Aluminum (Al)). In alternativeexamples, the plurality of lateral features 157 may be made of apatterned dielectric layer (e.g., a patterned layer of Silicon Nitride(SiN), Silicon Dioxide (SiO₂) or Silicon Carbide (SiC)). For exampleSilicon Nitride, and Silicon Dioxide may be deposited by reactivemagnetron sputtering from a silicon target in an appropriate atmosphere,for example Nitrogen, Oxygen or Carbon Dioxide. Silicon Carbide may besputtered from a Silicon Carbide target.

Once the plurality of lateral features 157 have been patterned (e.g.,patterned layer 157) as shown in FIG. 3A, sputter deposition ofsuccessive additional pairs of alternating layers of high acousticimpedance metal and low acoustic impedance metal may continue as shownin FIG. 3B by alternating sputtering from targets of high acousticimpedance metal and low acoustic impedance metal. For example,sputtering targets of high acoustic impedance metal such as Molybdenumor Tungsten may be used for sputtering the high acoustic impedance metallayers, and sputtering targets of low acoustic impedance metal such asAluminum or Titanium may be used for sputtering the low acousticimpedance metal layers. For example, the second pair of top metalelectrode layers, 141, 143, may be deposited by sputtering the lowacoustic impedance metal for a first bottom metal electrode layer 141 ofthe pair on the plurality of lateral features 157, and then sputteringthe high acoustic impedance metal for a second top metal electrode layer143 of the pair on the first layer 141 of the pair. Similarly, the thirdpair of top metal electrode layers, 145, 147, may then be deposited bysequentially sputtering from the low acoustic impedance metal target andthe high acoustic impedance metal target. Similarly, the fourth pair oftop metal electrodes 149, 151, may then be deposited by sequentiallysputtering from the low acoustic impedance metal target and the highacoustic impedance metal target. Respective layer thicknesses of topmetal electrode layers of the first, second, third and fourth pairs 137,139, 141, 143, 145, 147, 149, 151 may correspond to approximately aquarter wavelength (e.g., a quarter acoustic wavelength) at the resonantfrequency of the resonator (e.g., respective layer thickness of aboutsix hundred Angstroms (600 A) for the example 24 GHz resonator.)

As mentioned previously, and as shown in FIG. 3B, after the lateralfeatures 157 are formed (e.g., patterned layer 157), they may functionas a step feature template, so that subsequent top metal electrodelayers formed on top of the lateral features 157 may retain steppatterns imposed by step features of the lateral features 157. Forexample, the second pair of top metal electrode layers 141, 143, thethird pair of top metal electrode layers 145, 147, and the fourth pairof top metal electrodes 149, 151, may retain step patterns imposed bystep features of the lateral features 157.

After depositing layers of the fourth pair of top metal electrodes 149,151 as shown in FIG. 3B, suitable photolithographic masking and etchingmay be used to form a first portion of etched edge region 153C for thetop acoustic reflector 115 as shown in FIG. 3C. A notional heavy dashedline is used in FIG. 3C depicting the first portion of etched edgeregion 153C associated with the top acoustic reflector 115. The firstportion of etched edge region 153C may extend along the thicknessdimension T25 of the top acoustic reflector 115. The first portionetched edge region 153C may extend through (e.g., entirely through orpartially through) the top acoustic reflector 115. The first portion ofthe etched edge region 153C may extend through (e.g., entirely throughor partially through) the initial top metal electrode layer 135. Thefirst portion of the etched edge region 153C may extend through (e.g.,entirely through or partially through) the first pair of top metalelectrode layers 137, 139. The first portion of the etched edge region153C may extend through (e.g., entirely through or partially through)the optional mass load layer 155. The first portion of the etched edgeregion 153C may extend through (e.g., entirely through or partiallythrough) at least one of the lateral features 157 (e.g., throughpatterned layer 157). The first portion of etched edge region 153C mayextend through (e.g., entirely through or partially through) the secondpair of top metal electrode layers, 141,143. The first portion etchededge region 153C may extend through (e.g., entirely through or partiallythrough) the third pair of top metal electrode layers, 145, 147. Thefirst portion of etched edge region 153C may extend through (e.g.,entirely through or partially through) the fourth pair of top metalelectrode layers, 149, 151. Just as suitable photolithographic maskingand etching may be used to form the first portion of etched edge region153C at a lateral extremity the top acoustic reflector 115 as shown inFIG. 3C, such suitable photolithographic masking and etching maylikewise be used to form another first portion of a laterally opposingetched edge region 154C at an opposing lateral extremity the topacoustic reflector 115, e.g., arranged laterally opposing or oppositefrom the first portion of etched edge region 153C, as shown in FIG. 3C.The another first portion of the laterally opposing etched edge region154C may extend through (e.g., entirely through or partially through)the opposing lateral extremity of the top acoustic reflector 115, e.g.,arranged laterally opposing or opposite from the first portion of etchededge region 153C, as shown in FIG. 3C. The mesa structure (e.g., thirdmesa structure) corresponding to the top acoustic reflector 115 mayextend laterally between (e.g., may be formed between) etched edgeregion 153C and laterally opposing etched edge region 154C. Dry etchingmay be used, e.g., reactive ion etching may be used to etch thematerials of the top acoustic reflector. Chlorine based reactive ionetch may be used to etch Aluminum, in cases where Aluminum is used inthe top acoustic reflector. Fluorine based reactive ion etch may be usedto etch Tungsten (W), Molybdenum (Mo), Titanium (Ti), Silicon Nitride(SiN), Silicon Dioxide (SiO₂) and/or Silicon Carbide (SiC) in caseswhere these materials are used in the top acoustic reflector.

After etching to form the first portion of etched edge region 153C fortop acoustic reflector 115 as shown in FIG. 3C, additional suitablephotolithographic masking and etching may be used to form elongatedportion of etched edge region 153D for top acoustic reflector 115 andfor the stack 104 of four temperature compensating piezoelectric layers105, 107, 109, 111 as shown in FIG. 3D. A notional heavy dashed line isused in FIG. 3D depicting the elongated portion of etched edge region153D associated with the stack 104 of four temperature compensatingpiezoelectric layers 105, 107, 109, 111 and with the top acousticreflector 115. Accordingly, the elongated portion of etched edge region153D shown in FIG. 3D may extend through (e.g., entirely through orpartially through) the fourth pair of top metal electrode layers, 149,151, the third pair of top metal electrode layers, 145, 147, the secondpair of top metal electrode layers, 141,143, at least one of the lateralfeatures 157, (e.g., patterned layer 157), the optional mass load layer155, the first pair of top metal electrode layers 137, 139 and theinitial top metal electrode layer 135 of the top acoustic reflector 115.The elongated portion of etched edge region 153D may extend through(e.g., entirely through or partially through) the stack 104 of fourtemperature compensating piezoelectric layers 105, 107, 109, 111. Theelongated portion of etched edge region 153D may extend through (e.g.,entirely through or partially through) the first temperaturecompensating piezoelectric layer, 105, e.g., having the normal axisorientation, first interposer layer 159, first middle temperaturecompensating piezoelectric layer, 107, e.g., having the reverse axisorientation, second interposer layer 161, second middle interposerlayer, 109, e.g., having the normal axis orientation, third interposerlayer 163, and top temperature compensating piezoelectric layer 111,e.g., having the reverse axis orientation. The elongated portion ofetched edge region 153D may extend along the thickness dimension T25 ofthe top acoustic reflector 115. The elongated portion of etched edgeregion 153D may extend along the thickness dimension T27 of the stack104 of four temperature compensating piezoelectric layers 105, 107, 109,111. Just as suitable photolithographic masking and etching may be usedto form the elongated portion of etched edge region 153D at the lateralextremity the top acoustic reflector 115 and at a lateral extremity ofthe stack 104 of four temperature compensating piezoelectric layers 105,107, 109, 111 as shown in FIG. 3D, such suitable photolithographicmasking and etching may likewise be used to form another elongatedportion of the laterally opposing etched edge region 154D at theopposing lateral extremity the top acoustic reflector 115 and the stack104 of four temperature compensating piezoelectric layers 105, 107, 109,111, e.g., arranged laterally opposing or opposite from the elongatedportion of etched edge region 153D, as shown in FIG. 3D. The anotherelongated portion of the laterally opposing etched edge region 154D mayextend through (e.g., entirely through or partially through) theopposing lateral extremity of the top acoustic reflector 115 and thestack of four temperature compensating piezoelectric layers 105, 107,109, 111, e.g., arranged laterally opposing or opposite from theelongated portion of etched edge region 153D, as shown in FIG. 3D. Themesa structure (e.g., third mesa structure) corresponding to the topacoustic reflector 115 may extend laterally between (e.g., may be formedbetween) etched edge region 153D and laterally opposing etched edgeregion 154D. The mesa structure (e.g., first mesa structure)corresponding to stack 104 of the example four temperature compensatingpiezoelectric layers may extend laterally between (e.g., may be formedbetween) etched edge region 153D and laterally opposing etched edgeregion 154D. Dry etching may be used, e.g., reactive ion etching may beused to etch the materials of the stack 104 of four temperaturecompensating piezoelectric layers 105, 107, 109, 111 and any interposerlayers. For example, Chlorine based reactive ion etch may be used toetch Aluminum Nitride of the temperature compensating piezoelectriclayers. For example, Fluorine based reactive ion etch may be used toetch Tungsten (W), Molybdenum (Mo), Titanium (Ti), Silicon Nitride(SiN), Silicon Dioxide (SiO₂) and/or Silicon Carbide (SiC) in caseswhere these materials are used in layers of temperature compensatingmaterial and/or interposer layers.

After etching to form the elongated portion of etched edge region 153Dfor top acoustic reflector 115 and the stack 104 of four temperaturecompensating piezoelectric layers 105, 107, 109, 111 as shown in FIG.3D, further additional suitable photolithographic masking and etchingmay be used to form etched edge region 153D for top acoustic reflector115 and for the stack 104 of four temperature compensating piezoelectriclayers 105, 107, 109, 111 and for bottom acoustic reflector 113 as shownin FIG. 3E. The notional heavy dashed line is used in FIG. 3E depictingthe etched edge region 153 associated with the stack 104 of fourtemperature compensating piezoelectric layers 105, 107, 109, 111 andwith the top acoustic reflector 115 and with the bottom acousticreflector 113. The etched edge region 153 may extend along the thicknessdimension T25 of the top acoustic reflector 115. The etched edge region153 may extend along the thickness dimension T27 of the stack 104 offour temperature compensating piezoelectric layers 105, 107, 109, 111.The etched edge region 153 may extend along the thickness dimension T23of the bottom acoustic reflector 113. Just as suitable photolithographicmasking and etching may be used to form the etched edge region 153 atthe lateral extremity the top acoustic reflector 115 and at the lateralextremity of the stack 104 of four temperature compensatingpiezoelectric layers 105, 107, 109, 111 and at a lateral extremity ofthe bottom acoustic reflector 113 as shown in FIG. 3E, such suitablephotolithographic masking and etching may likewise be used to formanother laterally opposing etched edge region 154 at the opposinglateral extremity of the top acoustic reflector 115 and the stack 104 offour temperature compensating piezoelectric layers 105, 107, 109, 111,and the bottom acoustic reflector 113, e.g., arranged laterally opposingor opposite from the etched edge region 153, as shown in FIG. 3E. Thelaterally opposing etched edge region 154 may extend through (e.g.,entirely through or partially through) the opposing lateral extremity ofthe top acoustic reflector 115 and the stack of four temperaturecompensating piezoelectric layers 105, 107, 109, 111, and the bottomacoustic reflector 113 e.g., arranged laterally opposing or oppositefrom the etched edge region 153, as shown in FIG. 3E.

After the foregoing etching to form the etched edge region 153 and thelaterally opposing etched edge region 154 of the resonator 100 shown inFIG. 3E, a planarization layer 165 may be deposited. A suitableplanarization material (e.g., Silicon Dioxide (SiO₂), Hafnium Dioxide(HfO2), Polyimide, or BenzoCyclobutene (BCB)). These materials may bedeposited by suitable methods, for example, chemical vapor deposition,standard or reactive magnetron sputtering (e.g., in cases of SiO2 orHfO2) or spin coating (e.g., in cases of Polyimide or BenzoCyclobutene(BCB)). An isolation layer 167 may also be deposited over theplanarization layer 165. A suitable low dielectric constant (low-k), lowacoustic impedance (low-Za) material may be used for the isolation layer167, for example polyimide, or BenzoCyclobutene (BCB). These materialsmay be deposited by suitable methods, for example, chemical vapordeposition, standard or reactive magnetron sputtering or spin coating.After planarization layer 165 and the isolation layer 167 have beendeposited, additional procedures of photolithographic masking, layeretching, and mask removal may be done to form a pair of etchedacceptance locations 183A, 183B for electrical interconnections.Reactive ion etching or inductively coupled plasma etching with a gasmixture of argon, oxygen and a fluorine containing gas such astetrafluoromethane (CF4) or Sulfur hexafluoride (SF6) may be used toetch through the isolation layer 167 and the planarization layer 165 toform the pair of etched acceptance locations 183A, 183B for electricalinterconnections. Photolithographic masking, sputter deposition, andmask removal may then be used form electrical interconnects in the pairof etched acceptance locations 183A, 183B shown in FIG. 3E, so as toprovide for the bottom electrical interconnect 169 and top electricalinterconnect 171 that are shown explicitly in FIG. 1A. A suitablematerial, for example Gold (Au) may be used for the bottom electricalinterconnect 169 and top electrical interconnect 171.

FIGS. 4A through 4G show alternative example temperature compensatingbulk acoustic wave resonators 400A through 400G to the exampletemperature compensating bulk acoustic wave resonator 100A shown in FIG.1A. For example, the temperature compensating bulk acoustic waveresonator 400A, 400E shown in FIG. 4A, 4E may have a cavity 483A, 483E,e.g., an air cavity 483A, 483E, e.g., extending into substrate 401A,401E, e.g., extending into silicon substrate 401A, 401E, e.g., arrangedbelow bottom acoustic reflector 413A, 413E. The cavity 483A, 483E may beformed using techniques known to those with ordinary skill in the art.For example, the cavity 483A,483E may be formed by initialphotolithographic masking and etching of the substrate 401A, 401E (e.g.,silicon substrate 401A, 401E), and deposition of a sacrificial material(e.g., phosphosilicate glass (PSG)). The phosphosilicate glass (PSG) maycomprise 8% phosphorous and 92% silicon dioxide. The resonator 400A,400E may be formed over the sacrificial material (e.g., phosphosilicateglass (PSG)). The sacrificial material may then be selectively etchedaway beneath the resonator 400A, 400E, leaving cavity 483A, 483E beneaththe resonator 400A, 400E. For example phosphosilicate glass (PSG)sacrificial material may be selectively etched away by hydrofluoric acidbeneath the resonator 400A, 400E, leaving cavity 483A, 483E beneath theresonator 400A, 400E. The cavity 483A, 483E may, but need not, bearranged to provide acoustic isolation of the structures, e.g., bottomacoustic reflector 413A, 413E, e.g., stack 404A, 404E of temperaturecompensating piezoelectric layers, e.g., resonator 400A, 400E from thesubstrate 401A, 401E.

Similarly, in FIGS. 4B, 4C, 4F and 4G, a via 485B, 485C, 485F, 485G(e.g., through silicon via 485B, 485F, e.g., through silicon carbide via485C, 485G) may, but need not, be arranged to provide acoustic isolationof the structures, e.g., bottom acoustic reflector 413B, 413C, 413F,413G, e.g., stack 404B, 404C, 404F, 404G, of temperature compensatingpiezoelectric layers, e.g., resonator 400B, 400C, 400F, 400G from thesubstrate 401B, 401C, 401F, 401G. The via 485B, 485C, 485F, 485G (e.g.,through silicon via 485B, 485F, e.g., through silicon carbide via 485C,485G) may be formed using techniques (e.g., using photolithographicmasking and etching techniques) known to those with ordinary skill inthe art. For example, in FIGS. 4B and 4F, backside photolithographicmasking and etching techniques may be used to form the through siliconvia 485B, 485F, and an additional passivation layer 487B, 487F may bedeposited, after the resonator 400B, 400F is formed. For example, inFIGS. 4C and 4G, backside photolithographic masking and etchingtechniques may be used to form the through silicon carbide via 485C,485G, after the top acoustic reflector 415C, 415G and stack 404C, 404Gof temperature compensating piezoelectric layers are formed. In FIGS. 4Cand 4G, after the through silicon carbide via 485C, 485G, is formed,backside photolithographic masking and deposition techniques may be usedto form bottom acoustic reflector 413C, 413G, and additional passivationlayer 487C, 487G.

In FIGS. 4A, 4B, 4C, 4E, 4F, 4G, bottom acoustic reflector 413A, 413B,413C, 413E, 413F, 413G, may include the acoustically reflective bottomelectrode stack of the plurality of bottom metal electrode layers, inwhich thicknesses of the bottom metal electrode layers may be related towavelength (e.g., acoustic wavelength) at the main resonant frequency ofthe example resonator 400A, 400B, 400C, 400E, 400F, 400G. As mentionedpreviously herein, the layer thickness of the initial bottom metalelectrode layer 417A, 417B, 417C, 417E, 417F, 417G, may be about oneeighth of a wavelength (e.g., one eighth acoustic wavelength) at themain resonant frequency of the example resonator 400A. Respective layerthicknesses, (e.g., T01 through T04, explicitly shown in FIGS. 4A, 4B,4C) for members of the pairs of bottom metal electrode layers may beabout one quarter of the wavelength (e.g., one quarter acousticwavelength) at the main resonant frequency of the example resonators400A, 400B, 400C, 400E, 400F, 400G. Relatively speaking, in variousalternative designs of the example resonators 400A, 400B, 400C, 400E,400F, 400G, for relatively lower main resonant frequencies (e.g., fiveGigahertz (5 GHz)) and having corresponding relatively longerwavelengths (e.g., longer acoustic wavelengths), may have relativelythicker bottom metal electrode layers in comparison to other alternativedesigns of the example resonators 400A, 400B, 400C, 400E, 400F, 400G,for relatively higher main resonant frequencies (e.g., twenty-fourGigahertz (24 GHz)). There may be corresponding longer etching times toform, e.g., etch through, the relatively thicker bottom metal electrodelayers in designs of the example resonator 400A, 400B, 400C, 400E, 400F,400G, for relatively lower main resonant frequencies (e.g., fiveGigahertz (5 GHz)). Accordingly, in designs of the example resonators400A, 400B, 400C, 400E, 400F, 400G, for relatively lower main resonantfrequencies (e.g., five Gigahertz (5 GHz)) having the relatively thickerbottom metal electrode layers, there may (but need not) be an advantagein etching time in having a relatively fewer number (e.g., five (5)) ofbottom metal electrode layers, shown in 4A, 4B, 4C, 4E, 4F, 4G, incomparison to a relatively larger number (e.g., nine (9)) of bottommetal electrode layers, shown in FIGS. 1A and 1 n FIG. 4D. Therelatively larger number (e.g., nine (9)) of bottom metal electrodelayers, shown in FIGS. 1A and 1 n FIG. 4D may (but need not) provide forrelatively greater acoustic isolation than the relatively fewer number(e.g., five (5)) of bottom metal electrode layers. However, in FIGS. 4Aand 4E the cavity 483A, 483E, (e.g., air cavity 483A, 483E) may (butneed not) be arranged to provide acoustic isolation enhancement relativeto some designs without the cavity 483A, 483E. Similarly, in FIGS. 4B,4C, 4F, 4G, the via 483B, 483C, 483F, 483G, (e.g., through silicon via485B, 485F, e.g., through silicon carbide via 485C, 485G) may (but neednot) be arranged to provide acoustic isolation enhancement relative tosome designs without the via 483B, 483C, 483F, 483G.

In FIGS. 4A and 4E, the cavity 483A, 483E may (but need not) be arrangedto compensate for relatively lesser acoustic isolation of the relativelyfewer number (e.g., five (5)) of bottom metal electrode layers. In FIGS.4A and 4E, the cavity 483A, 483E may (but need not) be arranged toprovide acoustic isolation benefits, while retaining possible electricalconductivity improvements and etching time benefits of the relativelyfewer number (e.g., five (5)) of bottom metal electrode layers, e.g.,particularly in designs of the example resonator 400A, 400E, forrelatively lower main resonant frequencies (e.g., five Gigahertz (5GHz)). Similarly, in FIGS. 4B, 4C, 4F, 4G, the via 483B, 483C, 483F,483G, may (but need not) be arranged to compensate for relatively lesseracoustic isolation of the relatively fewer number (e.g., five (5)) ofbottom metal electrode layers. In FIGS. 4B, 4C, 4F, 4G, the via 483B,483C, 483F, 483G, may (but need not) be arranged to provide acousticisolation benefits, while retaining possible electrical conductivityimprovement benefits and etching time benefits of the relatively fewernumber (e.g., five (5)) of bottom metal electrode layers, e.g.,particularly in designs of the example resonator 400B, 400C, 400F, 400G,for relatively lower main resonant frequencies (e.g., five Gigahertz (5GHz), e.g., below six Gigahertz (6 GHz), e.g., below five Gigahertz (5GHz)).

FIGS. 4D through 4G show alternative example temperature compensatingbulk acoustic wave resonators 400D through 400G to the exampletemperature compensating bulk acoustic wave resonator 100A shown in FIG.1A, in which the top acoustic reflector, 415D through 415G, may comprisea lateral connection portion, 489D through 489G, (e.g., bridge portion,489D through 489G), of the top acoustic reflector, 415D through 415G. Agap, 491D through 491G, may be formed beneath the lateral connectionportion, 489D through 489G, (e.g., bridge portion, 489D through 489G),of the top acoustic reflector 415D through 415G. The gap, 491D through491G, may be arranged adjacent to the etched edge region, 453D through453G, of the example resonators 400D through 400G.

For example, the gap, 491D through 491G, may be arranged adjacent towhere the etched edge region, 453D through 453G, extends through (e.g.,extends entirely through or extends partially through) the stack 404Dthrough 404G, of temperature compensating piezoelectric layers, forexample along the thickness dimension T27 of the stack 404D through404G. For example, the gap, 491D through 491G, may be arranged adjacentto where the etched edge region, 453D through 453G, extends through(e.g., extends entirely through or extends partially through) the bottomtemperature compensating piezoelectric layer 405D through 405G. Forexample, the gap, 491D through 491G, may be arranged adjacent to wherethe etched edge region, 453D through 453G, extends through (e.g.,extends entirely through or extends partially through) the bottomtemperature compensating piezoelectric layer 405D through 405G. Forexample, the gap, 491D through 491G, may be arranged adjacent to wherethe etched edge region, 453D through 453G, extends through (e.g.,extends entirely through or extends partially through) the first middletemperature compensating piezoelectric layer 407D through 407G. Forexample, the gap, 491D through 491G, may be arranged adjacent to wherethe etched edge region, 453D through 453G, extends through (e.g.,extends entirely through or extends partially through) the second middletemperature compensating piezoelectric layer 409D through 409G. Forexample, the gap, 491D through 491G, may be arranged adjacent to wherethe etched edge region, 453D through 453G, extends through (e.g.,extends entirely through or extends partially through) the toptemperature compensating piezoelectric layer 411D through 411G. Forexample, the gap, 491D through 491G, may be arranged adjacent to wherethe etched edge region, 453D through 453G, extends through (e.g.,extends entirely through or extends partially through) one or moreinterposer layers (e.g., first interposer layer, 495D through 459G,second interposer layer, 461D through 461G, third interposer layer 411Dthrough 411G).

For example, as shown in FIGS. 4D through 4G, the gap, 491D through491G, may be arranged adjacent to where the etched edge region, 453Dthrough 453G, extends through (e.g., extends partially through) the topacoustic reflector 415D through 415G, for example partially along thethickness dimension T25 of the top acoustic reflector 415D through 415G.For example, the gap, 491D through 491G, may be arranged adjacent towhere the etched edge region, 453D through 453G, extends through (e.g.,extends entirely through or extends partially through) the initial topelectrode layer 435D through 435G. For example, the gap, 491D through491G, may be arranged adjacent to where the etched edge region, 453Dthrough 453G, extends through (e.g., extends entirely through or extendspartially through) the first member, 437D through 437G, of the firstpair of top electrode layers, 437D through 437G, 439D through 439G.

For example, as shown in FIGS. 4D through 4F, the gap, 491D through491F, may be arranged adjacent to where the etched edge region, 453Dthrough 453F, extends through (e.g., extends entirely through or extendspartially through) the bottom acoustic reflector 413D through 413F, forexample along the thickness dimension T23 of the bottom acousticreflector 413D through 413F. For example, the gap, 491D through 491F,may be arranged adjacent to where the etched edge region, 453D through453F, extends through (e.g., extends entirely through or extendspartially through) the initial bottom electrode layer 417D through 417F.For example, the gap, 491D through 491F, may be arranged adjacent towhere the etched edge region, 453D through 453F, extends through (e.g.,extends entirely through or extends partially through) the first pair ofbottom electrode layers, 419D through 419F, 421D through 421F. Forexample, the gap, 491D through 491F, may be arranged adjacent to wherethe etched edge region, 453D through 453F, extends through (e.g.,extends entirely through or extends partially through) the second pairof bottom electrode layers, 423D through 423F, 425D through 425F. Forexample, as shown in FIGS. 4D through 4F, the etched edge region, 453Dthrough 453F, may extend through (e.g., entirely through or partiallythrough) the bottom acoustic reflector, 413D through 413F, and through(e.g., entirely through or partially through) one or more of thetemperature compensating piezoelectric layers, 405D through 405F, 407Dthrough 407F, 409D through 409F, 411D through 411F, to the lateralconnection portion, 489D through 489G, (e.g., to the bridge portion,489D through 489G), of the top acoustic reflector, 415D through 415F.

As shown in FIGS. 4D-4G, lateral connection portion, 489D through 489G,(e.g., bridge portion, 489D through 489G), of top acoustic reflector,415D through 415G, may be a multilayer lateral connection portion, 415Dthrough 415G, (e.g., a multilayer metal bridge portion, 415D through415G, comprising differing metals, e.g., metals having differingacoustic impedances.) For example, lateral connection portion, 489Dthrough 489G, (e.g., bridge portion, 489D through 489G), of top acousticreflector, 415D through 415G, may comprise the second member, 439Dthrough 439G, (e.g., comprising the relatively high acoustic impedancemetal) of the first pair of top electrode layers, 437D through 437G,439D through 439G. For example, lateral connection portion, 489D through489G, (e.g., bridge portion, 489D through 489G), of top acousticreflector, 415D through 415G, may comprise the second pair of topelectrode layers, 441D through 441G, 443D through 443G.

Gap 491D-491G may be an air gap 491D-491G, or may be filled with arelatively low acoustic impedance material (e.g., BenzoCyclobutene(BCB)), which may be deposited using various techniques known to thosewith skill in the art. Gap 491D-491G may be formed by depositing asacrificial material (e.g., phosphosilicate glass (PSG)) after theetched edge region, 453D through 453G, is formed. The lateral connectionportion, 489D through 489G, (e.g., bridge portion, 489D through 489G),of top acoustic reflector, 415D through 415G, may then be deposited(e.g., sputtered) over the sacrificial material. The sacrificialmaterial may then be selectively etched away beneath the lateralconnection portion, 489D through 489G, (e.g., e.g., beneath the bridgeportion, 489D through 489G), of top acoustic reflector, 415D through415G, leaving gap 491D-491G beneath the lateral connection portion, 489Dthrough 489G, (e.g., beneath the bridge portion, 489D through 489G). Forexample the phosphosilicate glass (PSG) sacrificial material may beselectively etched away by hydrofluoric acid beneath the lateralconnection portion, 489D through 489G, (e.g., beneath the bridgeportion, 489D through 489G), of top acoustic reflector, 415D through415G, leaving gap 491D-491G beneath the lateral connection portion, 489Dthrough 489G, (e.g., beneath the bridge portion, 489D through 489G).

Although in various example resonators, 100A, 400A, 400B, 400D, 400E,400F, polycrystalline temperature compensating piezoelectric layers(e.g., polycrystalline Aluminum Nitride (AlN)) may be deposited (e.g.,by sputtering), in other example resonators 400C, 400G, alternativesingle crystal or near single crystal temperature compensatingpiezoelectric layers (e.g., single/near single crystal Aluminum Nitride(AlN)) may be deposited (e.g., by metal organic chemical vapordeposition (MOCVD)). Normal axis temperature compensating piezoelectriclayers (e.g., normal axis Aluminum Nitride (AlN) temperaturecompensating piezoelectric layers) may be deposited by MOCVD usingtechniques known to those with skill in the art. As discussed previouslyherein, the interposer layers may be deposited by sputtering, butalternatively may be deposited by MOCVD. Reverse axis temperaturecompensating piezoelectric layers (e.g., reverse axis Aluminum Nitride(AlN) temperature compensating piezoelectric layers) may likewise bedeposited via MOCVD. For the respective example resonators 400C, 400Gshown in FIGS. 4C and 4G, the alternating axis temperature compensatingpiezoelectric stack 404C, 404G comprised of temperature compensatingpiezoelectric layers 405C, 407C, 409C, 411C, 405G, 407G, 409G, 411G aswell as interposer layers 459C, 461C, 463C, 459G, 461G, 453G extendingalong stack thickness dimension T27 fabricated using MOCVD on a siliconcarbide substrate 401C, 401G. For example, aluminum nitride oftemperature compensating piezoelectric layers 405C, 407C, 409C, 411C,405G, 407G, 409G, 411G may grow nearly epitaxially on silicon carbide(e.g., 4H SiC) by virtue of the small lattice mismatch between the polaraxis aluminum nitride wurtzite structure and specific crystalorientations of silicon carbide. Alternative small lattice mismatchsubstrates may be used (e.g., sapphire, e.g., aluminum oxide). Byvarying the ratio of the aluminum and nitrogen in the depositionprecursors, an aluminum nitride film may be produced with the desiredpolarity (e.g., normal axis, e.g., reverse axis). For example, normalaxis aluminum nitride may be synthesized using MOCVD when a nitrogen toaluminum ratio in precursor gases approximately 1000. For example,reverse axis aluminum nitride may synthesized when the nitrogen toaluminum ratio is approximately 27000. In accordance with the foregoing,FIGS. 4C and 4G show MOCVD synthesized normal axis temperaturecompensating piezoelectric layer 405C, 405G, MOCVD synthesized reverseaxis temperature compensating piezoelectric layer 407C, 407G, MOCVDsynthesized normal axis temperature compensating piezoelectric layer409C, 409G, and MOCVD synthesized reverse axis temperature compensatingpiezoelectric layer 411C, 411G. For example, normal axis temperaturecompensating piezoelectric layer 405C, 405G may be synthesized by MOCVDin a deposition environment where the nitrogen to aluminum gas ratio isrelatively low, e.g., 1000 or less. Next an oxyaluminum nitride layer,459C at lower temperature, may be deposited by MOCVD that may reverseaxis (e.g., reverse axis polarity) of the growing aluminum nitride underMOCVD growth conditions, and has also been shown to be able to bedeposited by itself under MOCVD growth conditions. Increasing thenitrogen to aluminum ratio into the several thousands during the MOCVDsynthesis may enable the reverse axis temperature compensatingpiezoelectric layer 407C, 407G to be synthesized. Interposer layer 461C,461G may be an oxide layer such as, but not limited to, aluminum oxideor silicon dioxide. This oxide layer may be deposited in in a lowtemperature physical vapor deposition process such as sputtering or in ahigher temperature chemical vapor deposition process. Normal axistemperature compensating piezoelectric layer 409C, 409G may be grown byMOCVD on top of interposer layer 461C, 461G using growth conditionssimilar to the normal axis layer 405C, 405G, as discussed previously,namely MOCVD in a deposition environment where the nitrogen to aluminumgas ratio is relatively low, e.g., 1000 or less. Next an aluminumoxynitride, interposer layer 463C, 463G may be deposited in a lowtemperature MOCVD process followed by a reverse axis temperaturecompensating piezoelectric layer 411C, 411G, synthesized in a hightemperature MOCVD process and an atmosphere of nitrogen to aluminumratio in the several thousand range. Upon conclusion of thesedepositions, the temperature compensating piezoelectric stack 404C, 404Gshown in FIGS. 4C and 4G may be realized.

FIG. 5 shows a schematic of an example ladder filter 500A (e.g., SHF orEHF wave ladder filter 500A) using three series resonators of thetemperature compensating bulk acoustic wave resonator structure of FIG.1A (e.g., three temperature compensating bulk acoustic SHF or EHF waveresonators), and two mass loaded shunt resonators of the temperaturecompensating bulk acoustic wave resonator structure of FIG. 1A (e.g.,two mass loaded temperature compensating bulk acoustic SHF or EHF waveresonators), along with a simplified view of the three seriesresonators. Accordingly, the example ladder filter 500A (e.g., SHF orEHF wave ladder filter 500A) is an electrical filter, comprising aplurality of temperature compensating bulk acoustic wave (BAW)resonators, e.g., on a substrate, in which the plurality of BAWresonators may comprise a respective first layer (e.g., bottom layer) oftemperature compensating piezoelectric material having a respectivepiezoelectrically excitable resonance mode. The plurality of BAWresonators of the filter 500A may comprise a respective top acousticreflector (e.g., top acoustic reflector electrode) including arespective initial top metal electrode layer and a respective first pairof top metal electrode layers electrically and acoustically coupled withthe respective first layer (e.g., bottom layer) of temperaturecompensating piezoelectric material to excite the respectivepiezoelectrically excitable resonance mode at a respective resonantfrequency. For example, the respective top acoustic reflector (e.g., topacoustic reflector electrode) may include the respective initial topmetal electrode layer and the respective first pair of top metalelectrode layers, and the foregoing may have a respective peak acousticreflectivity in the Super High Frequency (SHF) band or the ExtremelyHigh Frequency (EHF) band that includes the respective resonantfrequency of the respective BAW resonator. The plurality of BAWresonators of the filter 500A may comprise a respective bottom acousticreflector (e.g., bottom acoustic reflector electrode) including arespective initial bottom metal electrode layer and a respective firstpair of bottom metal electrode layers electrically and acousticallycoupled with the respective first layer (e.g., bottom layer) oftemperature compensating piezoelectric material to excite the respectivepiezoelectrically excitable resonance mode at the respective resonantfrequency. For example, the respective bottom acoustic reflector (e.g.,bottom acoustic reflector electrode) may include the respective initialbottom metal electrode layer and the respective first pair of bottommetal electrode layers, and the foregoing may have a respective peakacoustic reflectivity in the Super High Frequency (SHF) band or theExtremely High Frequency (EHF) band that includes the respectiveresonant frequency of the respective BAW resonator. The respective firstlayer (e.g., bottom layer) of temperature compensating piezoelectricmaterial may be sandwiched between the respective top acoustic reflectorand the respective bottom acoustic reflector. Further, the plurality ofBAW resonators may comprise at least one respective additional layer oftemperature compensating piezoelectric material, e.g., first middletemperature compensating piezoelectric layer. The at least oneadditional layer of temperature compensating piezoelectric material mayhave the piezoelectrically excitable main resonance mode with therespective first layer (e.g., bottom layer) of temperature compensatingpiezoelectric material. The respective first layer (e.g., bottom layer)of temperature compensating piezoelectric material may have a respectivefirst temperature compensating piezoelectric axis orientation (e.g.,normal axis orientation) and the at least one respective additionallayer of temperature compensating piezoelectric material may have arespective piezoelectric axis orientation (e.g., reverse axisorientation) that opposes the first piezoelectric axis orientation ofthe respective first layer of temperature compensating piezoelectricmaterial. Further discussion of features that may be included in theplurality of BAW resonators of the filter 500A is present previouslyherein with respect to previous discussion of FIG. 1A

As shown in the schematic appearing at an upper section of FIG. 5, theexample ladder filter 500A may include an input port comprising a firstnode 521A (InA), and may include a first series resonator 501A(Series1A) (e.g., first temperature compensating bulk acoustic SHF orEHF wave resonator 501A) coupled between the first node 521A (InA)associated with the input port and a second node 522A. The exampleladder filter 500A may also include a second series resonator 502A(Series2A) (e.g., second temperature compensating bulk acoustic SHF orEHF wave resonator 502A) coupled between the second node 522A and athird node 523A. The example ladder filter 500A may also include a thirdseries resonator 503A (Series3A) (e.g., third temperature compensatingbulk acoustic SHF or EHF wave resonator 503A) coupled between the thirdnode 523A and a fourth node 524A (OutA), which may be associated with anoutput port of the ladder filter 500A. The example ladder filter 500Amay also include a first mass loaded shunt resonator 511A (Shunt1A)(e.g., first mass loaded temperature compensating bulk acoustic SHF orEHF wave resonator 511A) coupled between the second node 522A andground. The example ladder filter 500A may also include a second massloaded shunt resonator 512A (Shunt2A) (e.g., second mass loadedtemperature compensating bulk acoustic SHF or EHF wave resonator 512A)coupled between the third node 523 and ground.

Appearing at a lower section of FIG. 5 is the simplified view of thethree series resonators 501B (Series1B), 502B (Series2B), 503B(Series3B) in a serial electrically interconnected arrangement 500B, forexample, corresponding to series resonators 501A, 502A, 503A, of theexample ladder filter 500A. The three series resonators 501B (Series1B),502B (Series2B), 503B (Series3B), may be constructed as shown in thearrangement 500B and electrically interconnected in a way compatiblewith integrated circuit fabrication of the ladder filter. Although thefirst mass loaded shunt resonator 511A (Shunt1A) and the second massloaded shunt resonator 512A are not explicitly shown in the arrangement500B appearing at a lower section of FIG. 5, it should be understoodthat the first mass loaded shunt resonator 511A (Shunt1A) and the secondmass loaded shunt resonator 512A are constructed similarly to what isshown for the series resonators in the lower section of FIG. 5, but thatthe first and second mass loaded shunt resonators 511A, 512A may includemass layers, in addition to layers corresponding to those shown for theseries resonators in the lower section of FIG. 5 (e.g., the first andsecond mass loaded shunt resonators 511A, 512A may include respectivemass layers, in addition to respective top acoustic reflectors ofrespective top metal electrode layers, may include respectivealternating axis stacks of temperature compensating piezoelectricmaterial layers, and may include respective bottom acoustic reflectorsof bottom metal electrode layers.) For example, all of the resonators ofthe ladder filter may be co-fabricated using integrated circuitprocesses (e.g., Complementary Metal Oxide Semiconductor (CMOS)compatible fabrication processes) on the same substrate (e.g., samesilicon substrate). The example ladder filter 500A and serialelectrically interconnected arrangement 500B of series resonators 501A,502A, 503A, may respectively be relatively small in size, and mayrespectively have a lateral dimension (X5) of less than approximatelyone millimeter.

For example, the serial electrically interconnected arrangement 500B ofthree series resonators 501B (Series1B), 502B (Series2B), 503B(Series3B), may include an input port comprising a first node 521B (InB)and may include a first series resonator 501B (Series1B) (e.g., firsttemperature compensating bulk acoustic SHF or EHF wave resonator 501B)coupled between the first node 521B (InB) associated with the input portand a second node 522B. The first node 521B (InB) may include bottomelectrical interconnect 569B electrically contacting a first bottomacoustic reflector of first series resonator 501B (Series1B) (e.g.,first bottom acoustic reflector electrode of first series resonator 501B(Series1B)). Accordingly, in addition to including bottom electricalinterconnect 569, the first node 521B (InB) may also include the firstbottom acoustic reflector of first series resonator 501B (Series1B)(e.g., first bottom acoustic reflector electrode of first seriesresonator 501B (Series1B)). The first bottom acoustic reflector of firstseries resonator 501B (Series1B) (e.g., first bottom acoustic reflectorelectrode of first series resonator 501B (Series1B)) may include a stackof the plurality of bottom metal electrode layers 517 through 525. Theserial electrically interconnected arrangement 500B of three seriesresonators 501B (Series1B), 502B (Series2B), 503B (Series3B), mayinclude the second series resonator 502B (Series2B) (e.g., secondtemperature compensating bulk acoustic SHF or EHF wave resonator 502B)coupled between the second node 522B and a third node 523B. The thirdnode 523B may include a second bottom acoustic reflector of secondseries resonator 502B (Series2B) (e.g., second bottom acoustic reflectorelectrode of second series resonator 502B (Series2B)). The second bottomacoustic reflector of second series resonator 502B (Series2B) (e.g.,second bottom acoustic reflector electrode of second series resonator502B (Series2B)) may include an additional stack of an additionalplurality of bottom metal electrode layers. The serial electricallyinterconnected arrangement 500B of three series resonators 501B(Series1B), 502B (Series2B), 503B (Series3B), may also include the thirdseries resonator 503B (Series3B) (e.g., third temperature compensatingbulk acoustic SHF or EHF wave resonator 503B) coupled between the thirdnode 523B and a fourth node 524B (OutB). The third node 523B, e.g.,including the additional plurality of bottom metal electrode layers, mayelectrically interconnect the second series resonator 502B (Series2B)and the third series resonator 503B (Series3B). The second bottomacoustic reflector (e.g., second bottom acoustic reflector electrode) ofsecond series resonator 502B (Series2B) of the third node 523B, e.g.,including the additional plurality of bottom metal electrode layers, maybe a mutual bottom acoustic reflector (e.g., mutual bottom acousticreflector electrode), and may likewise serve as bottom acousticreflector (e.g., bottom acoustic reflector electrode) of third seriesresonator 503B (Series3B). The fourth node 524B (OutB) may be associatedwith an output port of the serial electrically interconnectedarrangement 500B of three series resonators 501B (Series1B), 502B(Series2B), 503B (Series3B). The fourth node 524B (OutB) may includeelectrical interconnect 571C.

The stack of the plurality of bottom metal electrode layers 517 through525 are associated with the first bottom acoustic reflector (e.g., firstbottom acoustic reflector electrode) of first series resonator 501B(Series1B). The additional stack of the additional plurality of bottommetal electrode layers (e.g., of the third node 523B) may be associatedwith the mutual bottom acoustic reflector (e.g., mutual bottom acousticreflector electrode) of both the second series resonant 502B (Series2B)and the third series resonator 503B (Series3B). Although stacks ofrespective five bottom metal electrode layers are shown in simplifiedview in FIG. 5, in should be understood that the stacks may includerespective larger numbers of bottom metal electrode layers, e.g.,respective nine top metal electrode layers. Further, the first seriesresonator (Series1B), and the second series resonant 502B (Series2B) andthe third series resonator 503B (Series3B) may all have the same, orapproximately the same, or different (e.g., achieved by means ofadditional mass loading layers) resonant frequency (e.g., the same, orapproximately the same, or different main resonant frequency). Forexample, small additional massloads (e.g, a tenth of the main shuntmass-load) of series and shunt resonators may help to reduce pass-bandripples in insertion loss, as may be appreciated by one with skill inthe art. The bottom metal electrode layers 517 through 525 and theadditional plurality of bottom metal electrode layers (e.g., of themutual bottom acoustic reflector, e.g., of the third node 523B) may haverespective thicknesses that are related to wavelength (e.g., acousticwavelength) for the resonant frequency (e.g., main resonant frequency)of the series resonators (e.g., first series resonator 501B (Series1B),e.g., second series resonator 502B, e.g., third series resonator(503B)). Various embodiments for series resonators (e.g., first seriesresonator 501B (Series1B), e.g., second series resonator 502B, e.g.,third series resonator (503B)) having various relatively higher resonantfrequency (e.g., higher main resonant frequency) may have relativelythinner bottom metal electrode thicknesses, e.g., scaled thinner withrelatively higher resonant frequency (e.g., higher main resonantfrequency). Similarly, various embodiments of the series resonators(e.g., first series resonator 501B (Series1B), e.g., second seriesresonator 502B, e.g., third series resonator (503B)) having variousrelatively lower resonant frequency (e.g., lower main resonantfrequency) may have relatively thicker bottom metal electrode layerthicknesses, e.g., scaled thicker with relatively lower resonantfrequency (e.g., lower main resonant frequency). The bottom metalelectrode layers 517 through 525 and the additional plurality of bottommetal electrode layers (e.g., of the mutual bottom acoustic reflector,e.g., of the third node 523B) may include members of pairs of bottommetal electrodes having respective thicknesses of one quarter wavelength(e.g., one quarter acoustic wavelength) at the resonant frequency (e.g.,main resonant frequency) of the series resonators (e.g., first seriesresonator 501B (Series1B), e.g., second series resonator 502B, e.g.,third series resonator (503B)). The stack of bottom metal electrodelayers 517 through 525 and the stack of additional plurality of bottommetal electrode layers (e.g., of the mutual bottom acoustic reflector,e.g., of the third node 523B) may include respective alternating stacksof different metals, e.g., different metals having different acousticimpedances (e.g., alternating relatively high acoustic impedance metalswith relatively low acoustic impedance metals). The foregoing mayprovide acoustic impedance mismatches for facilitating acousticreflectivity (e.g., SHF or EHF acoustic wave reflectivity) of the firstbottom acoustic reflector (e.g., first bottom acoustic reflectorelectrode) of the first series resonator 501B (Series1B) and the mutualbottom acoustic reflector (e.g., of the third node 523B) of the secondseries resonator 502B (Series2B) and the third series resonator 503B(Series3B).

A first top acoustic reflector (e.g., first top acoustic reflectorelectrode) comprises a first stack of a first plurality of top metalelectrode layers 535C through 543C of the first series resonator 501B(Series1B). A second top acoustic reflector (e.g., second top acousticreflector electrode) comprises a second stack of a second plurality oftop metal electrode layers 535D through 543D of the second seriesresonator 502B (Series2B). A third top acoustic reflector (e.g., thirdtop acoustic reflector electrode) comprises a third stack of a thirdplurality of top metal electrode layers 535E through 543E of the thirdseries resonator 503B (Series3B). Although stacks of respective five topmetal electrode layers are shown in simplified view in FIG. 5, it shouldbe understood that the stacks may include respective larger numbers oftop metal electrode layers, e.g., respective nine bottom metal electrodelayers. Further, the first plurality of top metal electrode layers 535Cthrough 543C, the second plurality of top metal electrode layers 535Dthrough 543D, and the third plurality of top metal electrode layers 535Ethrough 543E may have respective thicknesses that are related towavelength (e.g., acoustic wavelength) for the resonant frequency (e.g.,main resonant frequency) of the series resonators (e.g., first seriesresonator 501B (Series1B), e.g., second series resonator 502B, e.g.,third series resonator (503B)). Various embodiments for seriesresonators (e.g., first series resonator 501B (Series1B), e.g., secondseries resonator 502B, e.g., third series resonator (503B)) havingvarious relatively higher resonant frequency (e.g., higher main resonantfrequency) may have relatively thinner top metal electrode thicknesses,e.g., scaled thinner with relatively higher resonant frequency (e.g.,higher main resonant frequency). Similarly, various embodiments of theseries resonators (e.g., first series resonator 501B (Series1B), e.g.,second series resonator 502B, e.g., third series resonator (503B))having various relatively lower resonant frequency (e.g., lower mainresonant frequency) may have relatively thicker top metal electrodelayer thicknesses, e.g., scaled thicker with relatively lower resonantfrequency (e.g., lower main resonant frequency). The first plurality oftop metal electrode layers 535C through 543C, the second plurality oftop metal electrode layers 535D through 543D, and the third plurality oftop metal electrode layers 535E through 543E may include members ofpairs of bottom metal electrodes having respective thicknesses of onequarter wavelength (e.g., one quarter acoustic wavelength) of theresonant frequency (e.g., main resonant frequency) of the seriesresonators (e.g., first series resonator 501B (Series1B), e.g., secondseries resonator 502B, e.g., third series resonator (503B)). The firststack of the first plurality of top metal electrode layers 535C through543C, the second stack of the second plurality of top metal electrodelayers 535D through 543D, and the third stack of the third plurality oftop metal electrode layers 535E through 543E may include respectivealternating stacks of different metals, e.g., different metals havingdifferent acoustic impedances (e.g., alternating relatively highacoustic impedance metals with relatively low acoustic impedancemetals). The foregoing may provide acoustic impedance mismatches forfacilitating acoustic reflectivity (e.g., SHF or EHF acoustic wavereflectivity) of the top acoustic reflectors (e.g., the first topacoustic reflector of the first series resonator 501B (Series1B), e.g.,the second top acoustic reflector of the second series resonator 502B(Series2B), e.g., the third top acoustic reflector of the third seriesresonator 503B (Series3B)). Although not explicitly shown in the FIG. 5simplified views of metal electrode layers of the series resonators,respective pluralities of lateral features (e.g., respective pluralitiesof step features) may be sandwiched between metal electrode layers(e.g., between respective pairs of top metal electrode layers, e.g.,between respective first pairs of top metal electrode layers 537C, 539C,537D, 539D, 537E, 539E, and respective second pairs of top metalelectrode layers 541C, 543C, 541D, 543D, 541E, 543E. The respectivepluralities of lateral features may, but need not, limit parasiticlateral acoustic modes (e.g., facilitate suppression of spurious modes)of the temperature compensating bulk acoustic wave resonators of FIG. 5(e.g., of the series resonators, the mass loaded series resonators, andthe mass loaded shunt resonators).

The first series resonator 501B (Series1B) may comprise a firstalternating axis stack, e.g., an example first stack of four layers ofalternating axis temperature compensating piezoelectric material, 505Cthrough 511C. The second series resonator 502B (Series2B) may comprise asecond alternating axis stack, e.g., an example second stack of fourlayers of alternating axis temperature compensating piezoelectricmaterial, 505D through 511D. The third series resonator 503B (Series3B)may comprise a third alternating axis stack, e.g., an example thirdstack of four layers of alternating axis temperature compensatingpiezoelectric material, 505E through 511E. The first, second and thirdalternating axis temperature compensating piezoelectric stacks maycomprise layers of Aluminum Nitride (AlN) having alternating C-axiswurtzite structures and layers of temperature compensating material(e.g., comprising respective Silicon Dioxide layers, e.g., comprisingrespective metal sublayers over respective Silicon Dioxide (SiO₂)sublayers). For example, temperature compensating piezoelectric layers505C, 505D, 505E, 509C, 509D, 509E have normal axis orientation. Forexample, temperature compensating piezoelectric layers 507C, 507D, 507E,511C, 511D, 511E have reverse axis orientation. Members of the firststack of four layers of alternating axis temperature compensatingpiezoelectric material, 505C through 511C, and members of the secondstack of four layers of alternating axis temperature compensatingpiezoelectric material, 505D through 511D, and members of the thirdstack of four layers of alternating axis temperature compensatingpiezoelectric material, 505E through 511E, may have respectivethicknesses that are related to wavelength (e.g., acoustic wavelength)for the resonant frequency (e.g., main resonant frequency) of the seriesresonators (e.g., first series resonator 501B (Series1B), e.g., secondseries resonator 502B, e.g., third series resonator (503B)). Variousembodiments for series resonators (e.g., first series resonator 501B(Series1B), e.g., second series resonator 502B, e.g., third seriesresonator (503B)) having various relatively higher resonant frequency(e.g., higher main resonant frequency) may have relatively thinnertemperature compensating piezoelectric layer thicknesses, e.g., scaledthinner with relatively higher resonant frequency (e.g., higher mainresonant frequency). Similarly, various embodiments of the seriesresonators (e.g., first series resonator 501B (Series1B), e.g., secondseries resonator 502B, e.g., third series resonator (503B)) havingvarious relatively lower resonant frequency (e.g., lower main resonantfrequency) may have relatively thicker temperature compensatingpiezoelectric layer thicknesses, e.g., scaled thicker with relativelylower resonant frequency (e.g., lower main resonant frequency). Theexample first stack of four layers of alternating axis temperaturecompensating piezoelectric material, 505C through 511C, the examplesecond stack of four layers of alternating axis temperature compensatingpiezoelectric material, 505D through 511D and the example third stack offour layers of alternating axis temperature compensating piezoelectricmaterial, 505D through 511D may include stack members of temperaturecompensating piezoelectric layers having respective thicknesses ofapproximately one half wavelength (e.g., one half acoustic wavelength)at the resonant frequency (e.g., main resonant frequency) of the seriesresonators (e.g., first series resonator 501B (Series1B), e.g., secondseries resonator 502B, e.g., third series resonator (503B)).

The example first stack of four layers of alternating axis temperaturecompensating piezoelectric material, 505C through 511C, may include afirst interposer layer 566C of the first stack sandwiched between thefirst middle and second middle layers 507C, 509C of alternating axistemperature compensating piezoelectric material, 505C through 511C. Theexample second stack of four layers of alternating axis temperaturecompensating piezoelectric material, 505D through 511D, may include afirst interposer layer 566D of the second stack sandwiched between firstmiddle and second middle layers 507D, 509D of alternating axistemperature compensating piezoelectric material, 505D through 511D. Theexample third stack of four layers of alternating axis temperaturecompensating piezoelectric material, 505E through 511E, may include afirst interposer layer 566E of the third stack sandwiched between thefirst middle and second middle layers 507E, 509E of alternating axistemperature compensating piezoelectric material, 505E through 511E. Oneor more (e.g., one or a plurality of) interposer layers 566C, 566D, 566Emay be dielectric or metal interposer layers 566C, 566D, 566E. The metalinterposer layers 566C, 566D, 566E may be relatively high acousticimpedance metal interposer layers (e.g., using relatively high acousticimpedance metals such as Tungsten (W) or Molybdenum (Mo)). Such metalinterposer layers 566C, 566D, 566E may (but need not) flatten stressdistribution across adjacent piezoelectric layers, and may (but neednot) raise effective electromechanical coupling coefficient (Kt2) ofadjacent piezoelectric layers. Alternatively or additionally, one ormore (e.g., one or a plurality of) interposer layers 566C, 566D, 566Emay be dielectric interposer layers 566C, 566D, 566E. The dielectric ofthe dielectric interposer layers 566C, 566D, 566E may be a dielectricthat has a positive acoustic velocity temperature coefficient, soacoustic velocity increases with increasing temperature of thedielectric. The dielectric of the dielectric interposer layers 566C,566D, 566E may be, for example, silicon dioxide. Dielectric interposerlayers 566C, 566D, 566E may, but need not, facilitate compensating forfrequency response shifts with increasing temperature. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may comprise metal and dielectric for respective interposerlayers. The first series resonator 501B (Series1B), the second seriesresonator 502B (Series2B) and the third series resonator 503B (Series3B)may have respective etched edge regions 553C, 553D, 553E, and respectivelaterally opposing etched edge regions 554C, 554D, 554E. Reference ismade to resonator mesa structures as have already been discussed indetail previously herein. Accordingly, they are not discussed again indetail at this point. Briefly, respective first, second and third mesastructures of the respective first series resonator 501B (Series1B), therespective second series resonator 502B (Series2B) and the respectivethird series resonator 503B (Series3B) may extend between respectiveetched edge regions 553C, 553D, 553E, and respective laterally opposingetched edge regions 554C, 554D, 554E of the respective first seriesresonator 501B (Series1B), the respective second series resonator 502B(Series2B) and the respective third series resonator 503B (Series3B).The second bottom acoustic reflector of second series resonator 502B(Series2B) of the third node 523B, e.g., including the additionalplurality of bottom metal electrode layers may be a second mesastructure. For example, this may be a mutual second mesa structurebottom acoustic reflector 523B, and may likewise serve as bottomacoustic reflector of third series resonator 503B (Series3B).Accordingly, this mutual second mesa structure bottom acoustic reflector523B may extend between etched edge region 553E of the third seriesresonator 503B (Series3B) and the laterally opposing etched edge region554D of the third series resonator 503B (Series3B).

FIG. 6 shows a schematic of an example ladder filter 600A (e.g., SHF orEHF wave ladder filter 600A) using five series resonators of thetemperature compensating bulk acoustic wave resonator structure of FIG.1A (e.g., five temperature compensating bulk acoustic SHF or EHF waveresonators), and four mass loaded shunt resonators of the temperaturecompensating bulk acoustic wave resonator structure of FIG. 1A (e.g.,four mass loaded temperature compensating bulk acoustic SHF or EHF waveresonators), along with a simplified top view of the nine resonatorsinterconnected in the example ladder filter 600B, and lateral dimensionsof the example ladder filter 600B. As shown in the schematic appearingat an upper section of FIG. 6, the example ladder filter 600A mayinclude an input port comprising a first node 621A (InputA E1TopA), andmay include a first series resonator 601A (Ser1A) (e.g., firsttemperature compensating bulk acoustic SHF or EHF wave resonator 601A)coupled between the first node 621A (InputA E1TopA) associated with theinput port and a second node 622A (E1BottomA). The example ladder filter600A may also include a second series resonator 602A (Ser2A) (e.g.,second temperature compensating bulk acoustic SHF or EHF wave resonator602A) coupled between the second node 622A (E1BottomA) and a third node623A (E3TopA). The example ladder filter 600A may also include a thirdseries resonator 603A (Ser3A) (e.g., third temperature compensating bulkacoustic SHF or EHF wave resonator 603A) coupled between the third node623A (E3TopA) and a fourth node 624A (E2BottomA). The example ladderfilter 600A may also include a fourth series resonator 604A (Ser4A)(e.g., fourth temperature compensating bulk acoustic SHF or EHF waveresonator 604A) coupled between the fourth node 624A (E2BottomA) and afifth node 625A (E4TopA). The example ladder filter 600A may alsoinclude a fifth series resonator 605A (Ser5A) (e.g., fifth temperaturecompensating bulk acoustic SHF or EHF wave resonator 605A) coupledbetween the fifth node 625A (E4TopA) and a sixth node 626A (OutputAE4BottomA), which may be associated with an output port of the ladderfilter 600A. The example ladder filter 600A may also include a firstmass loaded shunt resonator 611A (Sh1A) (e.g., first mass loadedtemperature compensating bulk acoustic SHF or EHF wave resonator 611A)coupled between the second node 622A (E1BottomA) and a first groundingnode 631A (E2TopA). The example ladder filter 600A may also include asecond mass loaded shunt resonator 612A (Sh2A) (e.g., second mass loadedtemperature compensating bulk acoustic SHF or EHF wave resonator 612A)coupled between the third node 623A (E3TopA) and a second grounding node632A (E3BottomA). The example ladder filter 600A may also include athird mass loaded shunt resonator 613A (Sh3A) (e.g., third mass loadedtemperature compensating bulk acoustic SHF or EHF wave resonator 613A)coupled between the fourth node 624A (E2BottomA) and the first groundingnode 631A (E2TopA). The example ladder filter 600A may also include afourth mass loaded shunt resonator 614A (Sh4A) (e.g., fourth mass loadedtemperature compensating bulk acoustic SHF or EHF wave resonator 614A)coupled between the fifth node 625A (E4TopA) and the second groundingnode 632A (E3BottomA). The first grounding node 631A (E2TopA) and thesecond grounding node 632A (E3BottomA) may be interconnected to eachother, and may be connected to ground, through an additional groundingconnection (AdditionalConnection).

Appearing at a lower section of FIG. 6 is the simplified top view of thenine resonators interconnected in the example ladder filter 600B, andlateral dimensions of the example ladder filter 600B. The example ladderfilter 600B may include an input port comprising a first node 621B(InputA E1TopB), and may include a first series resonator 601B (Ser1B)(e.g., first temperature compensating bulk acoustic SHF or EHF waveresonator 601B) coupled between (e.g., sandwiched between) the firstnode 621B (InputA E1TopB) associated with the input port and a secondnode 622B (E1BottomB). The example ladder filter 600B may also include asecond series resonator 602B (Ser2B) (e.g., second temperaturecompensating bulk acoustic SHF or EHF wave resonator 602B) coupledbetween (e.g., sandwiched between) the second node 622B (E1BottomB) anda third node 623B (E3TopB). The example ladder filter 600B may alsoinclude a third series resonator 603B (Ser3B) (e.g., third temperaturecompensating bulk acoustic SHF or EHF wave resonator 603B) coupledbetween (e.g., sandwiched between) the third node 623B (E3TopB) and afourth node 624B (E2BottomB). The example ladder filter 600B may alsoinclude a fourth series resonator 604B (Ser4B) (e.g., fourth temperaturecompensating bulk acoustic SHF or EHF wave resonator 604B) coupledbetween (e.g., sandwiched between) the fourth node 624B (E2BottomB) anda fifth node 625B (E4TopB). The example ladder filter 600B may alsoinclude a fifth series resonator 605B (Ser5B) (e.g., fifth temperaturecompensating bulk acoustic SHF or EHF wave resonator 605B) coupledbetween (e.g., sandwiched between) the fifth node 625B (E4TopB) and asixth node 626B (OutputB E4BottomB), which may be associated with anoutput port of the ladder filter 600B. The example ladder filter 600Bmay also include a first mass loaded shunt resonator 611B (Sh1B) (e.g.,first mass loaded temperature compensating bulk acoustic SHF or EHF waveresonator 611B) coupled between (e.g., sandwiched between) the secondnode 622B (E1BottomB) and a first grounding node 631B (E2TopB). Theexample ladder filter 600B may also include a second mass loaded shuntresonator 612B (Sh2B) (e.g., second mass loaded temperature compensatingbulk acoustic SHF or EHF wave resonator 612B) coupled between (e.g.,sandwiched between) the third node 623B (E3TopB) and a second groundingnode 632B (E3BottomB). The example ladder filter 600B may also include athird mass loaded shunt resonator 613B (Sh3B) (e.g., third mass loadedtemperature compensating bulk acoustic SHF or EHF wave resonator 613B)coupled between (e.g., sandwiched between) the fourth node 624B(E2BottomB) and the first grounding node 631B (E2TopB). The exampleladder filter 600B may also include a fourth mass loaded shunt resonator614B (Sh4B) (e.g., fourth mass loaded temperature compensating bulkacoustic SHF or EHF wave resonator 614B) coupled between (e.g.,sandwiched between) the fifth node 625B (E4TopB) and the secondgrounding node 632B (E3BottomB). The first grounding node 631B (E2TopB)and the second grounding node 632B (E3BottomB) may be interconnected toeach other, and may be connected to ground, through an additionalgrounding connection, not shown in the lower section of FIG. 6. Theexample ladder filter 600B may respectively be relatively small in size,and may respectively have lateral dimensions (X6 by Y6) of less thanapproximately one millimeter by one millimeter.

FIG. 7 shows an schematic of example inductors modifying an examplelattice filter 700 using a first pair of series resonators 701A (Se1T),702A (Se2T), (e.g., two temperature compensating bulk acoustic SHF orEHF wave resonators) of the temperature compensating bulk acoustic waveresonator structure of FIG. 1A, a second pair of series resonators 701B(Se2B), 702B (Se2B), (e.g., two additional temperature compensating bulkacoustic SHF or EHF wave resonators) of the temperature compensatingbulk acoustic wave resonator structure of FIG. 1A and two pairs of crosscoupled mass loaded shunt resonators 701C (Sh1C), 702D (Sh2C), 703C(Sh3C), 704C (Sh4C), (e.g., four mass loaded temperature compensatingbulk acoustic SHF or EHF wave resonators) of the temperaturecompensating bulk acoustic wave resonator structure of FIG. 1A. As shownin the schematic of FIG. 7, the example inductor modified lattice filter700 may include a first top series resonator 701A (Se1T) (e.g., firsttop temperature compensating bulk acoustic SHF or EHF wave resonator701A) coupled between a first top node 721A and a second top node 722A.The example inductor modified lattice filter 700 may also include asecond top series resonator 702A (Se2T) (e.g., second top temperaturecompensating bulk acoustic SHF or EHF wave resonator 702A) coupledbetween the second top node 722A and a third top node 723A.

The example inductor modified lattice filter 700 may include a firstbottom series resonator 701B (Se1B) (e.g., first bottom temperaturecompensating bulk acoustic SHF or EHF wave resonator 701B) coupledbetween a first bottom node 721B and a second bottom node 722B. Theexample inductor modified lattice filter 700 may also include a secondbottom series resonator 702B (Se2B) (e.g., second bottom temperaturecompensating bulk acoustic SHF or EHF wave resonator 702B) coupledbetween the second bottom node 722B and a third bottom node 723B. Theexample inductor modified lattice filter 700 may include a firstcross-coupled mass loaded shunt resonator 701C (Sh1C) (e.g., first massloaded temperature compensating bulk acoustic SHF or EHF wave resonator701C) coupled between the first top node 721A and the second bottom node722B. The example inductor modified lattice filter 700 may also includea second cross-coupled mass loaded shunt resonator 702C (Sh2C) (e.g.,second mass loaded temperature compensating bulk acoustic SHF or EHFwave resonator 702C) coupled between the second top node 722A and thefirst bottom node 721B. The example inductor modified lattice filter 700may include a third cross-coupled mass loaded shunt resonator 703C(Sh3C) (e.g., third mass loaded temperature compensating bulk acousticSHF or EHF wave resonator 703C) coupled between the second top node 722Aand the third bottom node 723B. The example inductor modified latticefilter 700 may also include a fourth cross-coupled mass loaded shuntresonator 704C (Sh4C) (e.g., fourth mass loaded temperature compensatingbulk acoustic SHF or EHF wave resonator 704C) coupled between the thirdtop node 723A and the second bottom node 722B. The example inductormodified lattice filter 700 may include a first inductor 711 (L1)coupled between the first top node 721A and the first bottom node 721B.The example inductor modified lattice filter 700 may include a secondinductor 712 (L2) coupled between the second top node 722A and thesecond bottom node 722B. The example inductor modified lattice filter700 may include a third inductor 713 (L3) coupled between the third topnode 723A and the third bottom node 723B.

FIGS. 8A and 8B show an example oscillator 800A, 800B (e.g., millimeterwave oscillator 800A, 800B, e.g., Super High Frequency (SHF) waveoscillator 800A, 800B, e.g., Extremely High Frequency (EHF) waveoscillator 800A, 800B) using the temperature compensating bulk acousticwave resonator structure of FIG. 1A. For example, FIGS. 8A and 8B showssimplified views of temperature compensating bulk acoustic waveresonator 801A, 801B electrically coupled with electrical oscillatorcircuitry (e.g., active oscillator circuitry 802A, 802B) through phasecompensation circuitry 803A, 803B (Φcomp). The example oscillator 800A,800B may be a negative resistance oscillator, e.g., in accordance with aone-port model as shown in FIGS. 8A and 8B. The electrical oscillatorcircuitry, e.g., active oscillator circuitry, may include one or moresuitable active devices (e.g., one or more suitably configuredamplifying transistors) to generate a negative resistance commensuratewith resistance of the temperature compensating bulk acoustic waveresonator 801A, 801B. In other words, energy lost in temperaturecompensating bulk acoustic wave resonator 801A, 801B may be replenishedby the active oscillator circuitry, thus allowing steady oscillation,e.g., steady SHF or EHF wave oscillation. To ensure oscillationstart-up, active gain (e.g., negative resistance) of active oscillatorcircuitry 802A, 802B may be greater than one. As illustrated on opposingsides of a notional dashed line in FIGS. 8A and 8B, the activeoscillator circuitry 802A, 802B may have a complex reflectioncoefficient of the active oscillator circuitry (Tamp), and thetemperature compensating bulk acoustic wave resonator 801A, 801Btogether with the phase compensation circuitry 803A, 803B (Dcomp) mayhave a complex reflection coefficient (Γres). To provide for the steadyoscillation, e.g., steady SHF or EHF wave oscillation, a magnitude maybe greater than one for |Γamp Γres|, e.g., magnitude of a product of thecomplex reflection coefficient of the active oscillator circuitry (Γamp)and the complex reflection coefficient (Γres) of the resonator totemperature compensating bulk acoustic wave resonator 801A, 801Btogether with the phase compensation circuitry 803A, 803B (Dcomp) may begreater than one. Further, to provide for the steady oscillation, e.g.,steady SHF or EHF wave oscillation, phase angle may be an integermultiple of three-hundred-sixty degrees for Z Γamp Γres, e.g., a phaseangle of the product of the complex reflection coefficient of the activeoscillator circuitry (Γamp) and the complex reflection coefficient(Γres) of the resonator to temperature compensating bulk acoustic waveresonator 801A, 801B together with the phase compensation circuitry803A, 803B (Dcomp) may be an integer multiple of three-hundred-sixtydegrees. The foregoing may be facilitated by phase selection, e.g.,electrical length selection, of the phase compensation circuitry 803A,803B (Dcomp).

In the simplified view of FIG. 8A, the temperature compensating bulkacoustic wave resonator 801A (e.g., temperature compensating bulkacoustic SHF or EHF wave resonator) includes first normal axistemperature compensating piezoelectric layer 805A, first reverse axistemperature compensating piezoelectric layer 807A, and another normalaxis temperature compensating piezoelectric layer 809A, and anotherreverse axis temperature compensating piezoelectric layer 811A arrangedin a four temperature compensating piezoelectric layer alternating axisstack arrangement sandwiched between multilayer metal acoustic SHF orEHF wave reflector top electrode 815A and multilayer metal acoustic SHFor EHF wave reflector bottom electrode 813A. An output 816A of theoscillator 800A may be coupled to the temperature compensating bulkacoustic wave resonator 801A (e.g., coupled to multilayer metal acousticSHF or EHF wave reflector top electrode 815A). It should be understoodthat a first interposer layer 866A as discussed previously herein withrespect to FIG. 1A is explicitly shown in the simplified view theexample temperature compensating bulk acoustic wave resonator 801A shownin FIG. 8A. The first interposer layer 866A may be included andinterposed between adjacent piezoelectric layers. For example, the firstinterposer layer 866A may be arranged between first middle normal axistemperature compensating piezoelectric layer 807A and second middlenormal axis piezoelectric layer 809A. As discussed previously herein,such first interposer 866A may be metal or dielectric, and may, but neednot provide various benefits, as discussed previously herein.Alternatively or additionally, any interposer layers may comprise metaland dielectric.

A notional heavy dashed line is used in depicting an etched edge region853A associated with example resonator 801A. The example resonator 801Amay also include a laterally opposing etched edge region 854A arrangedopposite from the etched edge region 853A. The etched edge region 853A(and the laterally opposing etch edge region 854A) may similarly extendthrough various members of the example resonator 801A of FIG. 8A, in asimilar fashion as discussed previously herein with respect to theetched edge region 253D (and the laterally opposing etch edge region254D) of example resonator 2001D shown in FIG. 2B. As shown in FIG. 8A,a first mesa structure corresponding to the stack of four temperaturecompensating piezoelectric material layers 805A, 807A, 809A, 811A mayextend laterally between (e.g., may be formed between) etched edgeregion 853A and laterally opposing etched edge region 854A. A secondmesa structure corresponding to multilayer metal acoustic SHF or EHFwave reflector bottom electrode 813A may extend laterally between (e.g.,may be formed between) etched edge region 853A and laterally opposingetched edge region 854A. Third mesa structure corresponding tomultilayer metal acoustic SHF or EHF wave reflector top electrode 815Amay extend laterally between (e.g., may be formed between) etched edgeregion 853A and laterally opposing etched edge region 854A. Although notexplicitly shown in the FIG. 8A simplified view of metal electrodelayers, e.g., multilayer metal acoustic SHF or EHF wave reflector topelectrode 815A, a plurality of lateral features (e.g., plurality of stepfeatures, e.g., patterned layer) may be sandwiched between metalelectrode layers (e.g., between pairs of top metal electrode layers. Theplurality of lateral features may, but need not, limit parasitic lateralacoustic modes (e.g., facilitate suppression of spurious modes) of theexample temperature compensating bulk acoustic wave resonator of FIG.8A.

General structures and applicable teaching of this disclosure for themultilayer metal acoustic SHF or EHF reflector top electrode 815A andthe multilayer metal acoustic SHF or EHF reflector bottom electrode 813Ahave already been discussed in detail previously herein with respect ofFIGS. 1A and 4A through 4G, which for brevity are incorporated byreference rather than repeated fully here. As already discussed, thesestructures are directed to respective pairs of metal electrode layers,in which a first member of the pair has a relatively low acousticimpedance (relative to acoustic impedance of an other member of thepair), in which the other member of the pair has a relatively highacoustic impedance (relative to acoustic impedance of the first memberof the pair), and in which the respective pairs of metal electrodelayers have layer thicknesses corresponding to approximately one quarterwavelength (e.g., approximately one quarter acoustic wavelength) at amain resonant frequency of the resonator. Accordingly, it should beunderstood that the bulk acoustic SHF or EHF wave resonator 801A shownin FIG. 8A may include multilayer metal acoustic SHF or EHF wavereflector top electrode 815A and multilayer metal acoustic SHF or EHFwave reflector bottom electrode 815B in which the respective pairs ofmetal electrode layers may include layer thicknesses corresponding toapproximately a quarter wavelength (e.g., approximately one quarter ofan acoustic wavelength) at a SHF or EHF wave main resonant frequency ofthe bulk acoustic SHF or EHF wave resonator 801A. Initial top metalelectrode layer 835A and initial bottom metal electrode layer 817A mayhave respective layer thickness of about one eighth of a wavelength(e.g., one eighth of an acoustic wavelength) at the main resonantfrequency of the bulk acoustic SHF or EHF wave resonator 801A. Themultilayer metal acoustic SHF or EHF wave reflector top electrode 815Amay include the initial top metal electrode layer 835A and the firstpair of top metal electrode layers 824A electrically and acousticallycoupled with the four temperature compensating piezoelectric layeralternating axis stack arrangement (e.g., with the first normal axistemperature compensating piezoelectric layer 805A, e.g., with firstreverse axis temperature compensating piezoelectric layer 807A, e.g.,with another normal axis temperature compensating piezoelectric layer809A, e.g., with another reverse axis temperature compensatingpiezoelectric layer 811A) to excite the temperature compensatingpiezoelectrically excitable resonance mode at the resonant frequency.For example, the multilayer metal acoustic SHF or EHF wave reflector topelectrode 815A may include the initial top metal electrode layer 835Aand the first pair of top metal electrode layers 824A, and the foregoingmay have a respective peak acoustic reflectivity in the Super HighFrequency (SHF) band or the Extremely High Frequency (EHF) band thatincludes the respective resonant frequency of the respective BAWresonator. The multilayer metal acoustic SHF or EHF wave reflector topelectrode 815A may include a first mass patterned layer 857A. The firstpair of top metal electrodes 824A may be interposed between the firstpatterned layer 857A and a stack of layers of temperature compensatingpiezoelectric material including the first layer of temperaturecompensating piezoelectric material 805A (e.g., normal axis layer oftemperature compensating piezoelectric material 805A) and the secondlayer of temperature compensating piezoelectric material 807A (e.g.,reverse axis layer of temperature compensating piezoelectric material807A). First and second patterned layers 857A, 858A (e.g., top patternedlayer 857A and bottom patterned layer 858A) may contribute substantiallydifferently to facilitating spurious mode suppression in the bulkacoustic wave resonator 801A for oscillator 800A. In accordance with theteachings of this disclosure, one of the patterned layers (e.g., secondpatterned layer 858A, e.g., bottom patterned layer 858A) may be arrangedsubstantially nearer to a temperature compensating piezoelectric layerstack including the first and second layers of temperature compensatingpiezoelectric material than another one of the mass load layers (e.g.,first patterned layer 857A, e.g., top patterned layer 857A), tocontribute more to facilitating spurious mode suppression for bulkacoustic wave resonator 801A for oscillator 800A than what the anotherone of the patterned layers contributes.

Similarly, the multilayer metal acoustic SHF or EHF wave reflectorbottom electrode 813A may include the initial bottom metal electrodelayer 817A and the first pair of bottom metal electrode layers 822Aelectrically and acoustically coupled with the four temperaturecompensating piezoelectric layer alternating axis stack arrangement(e.g., with the first normal axis temperature compensating piezoelectriclayer 805A, e.g, with first reverse axis temperature compensatingpiezoelectric layer 807A, e.g., with another normal axis temperaturecompensating piezoelectric layer 809A, e.g., with another reverse axistemperature compensating piezoelectric layer 811A) to excite thetemperature compensating piezoelectrically excitable resonance mode atthe resonant frequency. For example, the multilayer metal acoustic SHFor EHF wave reflector bottom electrode 817A may include the initialbottom metal electrode layer 817A and the first pair of bottom metalelectrode layers 822A, and the foregoing may have a respective peakacoustic reflectivity in the Super High Frequency (SHF) band or theExtremely High Frequency (EHF) band that includes the resonant frequencyof the BAW resonator 801A. The second patterned layer 858A may beinterposed between the first pair of bottom metal electrodes 822A andthe initial bottom metal electrode layer 817A.

FIG. 8B shows a schematic of and example circuit implementation of theoscillator shown in FIG. 8A. Active oscillator circuitry 802B mayinclude active elements, symbolically illustrated in FIG. 8B byalternating voltage source 804B (Vs) coupled through negative resistance806B (Rneg), e.g., active gain element 806B, to example temperaturecompensating bulk acoustic wave resonator 801B (e.g., temperaturecompensating bulk acoustic SHF or EHF wave resonator) via phasecompensation circuitry 803B (Dcomp). The representation of exampletemperature compensating bulk acoustic wave resonator 801B (e.g.,temperature compensating bulk acoustic SHF or EHF wave resonator) mayinclude passive elements, symbolically illustrated in FIG. 8B byelectrode ohmic loss parasitic series resistance 808B (Rs), motionalcapacitance 810B (Cm), acoustic loss motional resistance 812B (Rm),motional inductance 814B (Lm), static or plate capacitance 816B (Co),and acoustic loss parasitic 818B (Ro). An output 816B of the oscillator800B may be coupled to the temperature compensating bulk acoustic waveresonator 801B (e.g., coupled to a multilayer metal acoustic SHF or EHFwave reflector top electrode of temperature compensating bulk acousticwave resonator 801B).

FIGS. 9A and 9B are simplified diagrams of a frequency spectrumillustrating application frequencies and application frequency bands ofthe example temperature compensating bulk acoustic wave resonators shownin FIG. 1A and FIGS. 4A through 4G, and the example filters shown inFIGS. 5 through 7, and the example oscillators shown in FIGS. 8A and 8B.A widely used standard to designate frequency bands in the microwaverange by letters is established by the United States Institute ofElectrical and Electronic Engineers (IEEE). In accordance with standardspublished by the IEEE, as defined herein, and as shown in FIGS. 9A and9B are application bands as follows: S Band (2 GHz-4 GHz), C Band (4GHz-8 GHz), X Band (8 GHz-12 GHz), Ku Band (12 GHz-18 GHz), K Band (18GHz-27 GHz), Ka Band (27 GHz-40 GHz), V Band (40 GHz-75 GHz), and W Band(75 GHz-110 GHz). FIG. 9A shows a first frequency spectrum portion 9000Ain a range from three Gigahertz (3 GHz) to eight Gigahertz (8 GHz),including application bands of S Band (2 GHz-4 GHz) and C Band (4 GHz-8GHz). As described subsequently herein, the 3rd Generation PartnershipProject standards organization (e.g., 3GPP) has standardized various 5Gfrequency bands. For example, included is a first application band 9010(e.g., 3GPP 5G n77 band) (3.3 GHz-4.2 GHz) configured for fifthgeneration broadband cellular network (5G) applications. As describedsubsequently herein, the first application band 9010 (e.g., 5G n77 band)includes a 5G sub-band 9011 (3.3 GHz-3.8 GHz). The 3GPP 5G sub-band 9011includes Long Term Evolution broadband cellular network (LTE)application sub-bands 9012 (3.4 GHz-3.6 GHz), 9013 (3.6 GHz-3.8 GHz),and 9014 (3.55 GHz-3.7 GHz). A second application band 9020 (4.4 GHz-5.0GHz) includes a sub-band 9021 for China specific applications. Discussednext are Unlicensed National Information Infrastructure (UNII) bands. Athird application band 9030 includes a UNII-1 band 9031 (5.15 GHz-5.25GHz) and a UNII-2A band 9032 (5.25 GHz 5.33 GHz). An LTE band 9033 (LTEBand 252) overlaps the same frequency range as the UNII-1 band 6031. Afourth application band 9040 includes a UNII-2C band 9041 (5.490GHz-5.735 GHz), a UNII-3 band 9042 (5.735 GHz-5.85 GHz), a UNII-4 band9043 (5.85 GHz-5.925 GHz), a UNII-5 band 9044 (5.925 GHz-6.425 GHz), aUNII-6 band 9045 (6.425 GHz-6.525 GHz), a UNII-7 band 9046 (6.525Ghz-6.875 Ghz), and a UNII-8 band 9047 (6.875 GHz-7125 Ghz). An LTE band9048 overlaps the same frequency range (5.490 GHz-5.735 GHz) as theUNII-3 band 9042. A sub-band 9049A shares the same frequency range asthe UNII-4 band 9043. An LTE band 9049B shares a subsection of the samefrequency range (5.855 GHz-5.925 GHz).

FIG. 9B shows a second frequency spectrum portion 9000B in a range fromeight Gigahertz (8 GHz) to one-hundred and ten Gigahertz (110 GHz),including application bands of X Band (8 Ghz-12 Ghz), Ku Band (12 Ghz-18Ghz), K Band (18 Ghz-27 Ghz), Ka Band (27 Ghz-40 Ghz), V Band (40 Ghz-75Ghz), and W Band (75 Ghz-110 Ghz). A fifth application band 9050includes 3GPP 5G bands configured for fifth generation broadbandcellular network (5G) applications, e.g., 3GPP 5G n258 band 9051 (24.25GHz-27.5 GHz), e.g., 3GPP 5G n261 band 9052 (27.5 GHz-28.35 GHz), e.g.,3GPP 5G n257 band 9053 (26.5 GHz-29.5). A sixth application band 9060includes the 3GPP 5G n260 band 9060 (37 GHz-40 GHz). A seventhapplication band 9070 includes United States WiGig Band for IEEE802.11ad and IEEE 802.11ay 9071 (57 GHz-71 Ghz), European Union andJapan WiGig Band for IEEE 802.11ad and IEEE 802.11ay 9072 (57 GHz-66Ghz), South Korea WiGig Band for IEEE 802.11ad and IEEE 802.11ay 9073(57 GHz-64 Ghz), and China WiGig Band for IEEE 802.11ad and IEEE802.11ay 9074 (59 GHz-64 GHz). An eighth application band 9080 includesan automobile radar band 9080 (76 GHz-81 GHz).

Accordingly, it should be understood from the foregoing that thetemperature compensating acoustic wave devices (e.g., resonators, e.g.,filters, e.g., oscillators) of this disclosure may be implemented in therespective application frequency bands just discussed. For example, thelayer thicknesses of the acoustic reflector electrodes and, for example,thicknesses of temperature compensating piezoelectric layers inalternating axis arrangement for the example temperature compensatingacoustic wave devices (e.g., the example 24 GHz temperature compensatingbulk acoustic wave resonators) of this disclosure may be scaled up anddown as needed to be implemented in the respective application frequencybands just discussed. This is likewise applicable to the example filters(e.g., temperature compensating bulk acoustic wave based filters) andexample oscillators (e.g., temperature compensating bulk acoustic waveresonator based oscillators) of this disclosure to be implemented in therespective application frequency bands just discussed. For example, thelayer thicknesses of the acoustic reflector electrodes, for example,thickness of temperature compensating piezoelectric layers inalternating axis arrangement of temperature compensating acoustic wavedevices of this disclosure (e.g., resonators, e.g., filters, e.g.,oscillators) may be sufficiently thin to select the respective resonantfrequency in the respective application frequency bands just discussed.The following examples pertain to further embodiments for temperaturecompensating acoustic wave devices, including but not limited to, e.g.,temperature compensating bulk acoustic wave resonators, e.g., filtersincorporating such temperature compensating bulk acoustic waveresonators, e.g., oscillators incorporating such temperaturecompensating bulk acoustic wave resonators, and from which numerouspermutations and configurations will be apparent. A first example is anacoustic wave device comprising a first temperature compensating layerof piezoelectric material having a piezoelectrically excitable resonancemode, and having a thickness so that the acoustic wave device has aresonant frequency, and an acoustic reflector electrode including afirst pair of metal electrode layers electrically and acousticallycoupled with the first layer of temperature compensating piezoelectricmaterial to excite the piezoelectrically excitable resonance mode at theresonant frequency. A second example is an acoustic wave device asdescribed in the first example, in which the resonant frequency of theacoustic wave device is in a 3rd Generation Partnership Project (3GPP)band. A third example is an acoustic wave device as described in thefirst example in which a frequency of a peak acoustic reflectivity ofthe first pair of top metal electrode layers is in a 3rd GenerationPartnership Project (3GPP) band. A fourth example is an acoustic wavedevice as the first example, in which the resonant frequency of theacoustic wave device is in a 3GPP n77 band 9010 as shown in FIG. 9A. Afifth example is an acoustic wave device as described in the firstexample, in which the resonant frequency of the acoustic wave device isin a 3GPP n79 band 9020 as shown in FIG. 9A. A sixth example is anacoustic wave device as described in the first example, in which theresonant frequency of the acoustic wave device is in a 3GPP n258 band9051 as shown in FIG. 9B. A seventh example is an acoustic wave deviceas described in the first example, in which the resonant frequency ofthe acoustic wave device is in a 3GPP n261 band 9052 as shown in FIG.9B. An eighth example is an acoustic wave device as described in thefirst example, in which the resonant frequency of the acoustic wavedevice is in a 3GPP n260 band 9060 as shown in FIG. 9B. A ninth exampleis an acoustic wave device as described in the first example, in whichthe resonant frequency of the acoustic wave device is in an Institute ofElectrical and Electronic Engineers (IEEE) C band as shown in FIG. 9A. Atenth example is an acoustic wave device as described in the firstexample, in which the resonant frequency of the acoustic wave device isin an Institute of Electrical and Electronic Engineers (IEEE) X band asshown in FIG. 9B. An eleventh example is an acoustic wave device asdescribed in the first example, in which the resonant frequency of theacoustic wave device is in an Institute of Electrical and ElectronicEngineers (IEEE) Ku band as shown in FIG. 9B. An twelfth example is anacoustic wave device as described in the first example, in which theresonant frequency of the acoustic wave device is in an Institute ofElectrical and Electronic Engineers (IEEE) K band as shown in FIG. 9B. Athirteenth example is an acoustic wave device as described in the firstexample, in which the resonant frequency of the acoustic wave device isin an Institute of Electrical and Electronic Engineers (IEEE) Ka band asshown in FIG. 9B. A fourteenth example is an acoustic wave device asdescribed in the first example, in which the resonant frequency of theacoustic wave device is in an Institute of Electrical and ElectronicEngineers (IEEE) V band as shown in FIG. 9B. A fifteenth example is anacoustic wave device as described in the first example, in which theresonant frequency of the acoustic wave device is in an Institute ofElectrical and Electronic Engineers (IEEE) W band as shown in FIG. 9B. Asixteenth example is an acoustic wave device as described in the firstexample, in which the resonant frequency of the acoustic wave device isin UNII-1 band 9031, as shown in FIG. 9A. A seventeenth example is anacoustic wave device as described in the first example, in which theresonant frequency of the acoustic wave device is in UNII-2A band 9032,as shown in FIG. 9A. A eighteenth example is an acoustic wave device asdescribed in the first example, in which the resonant frequency of theacoustic wave device is in UNII-2C band 9041, as shown in FIG. 9A. Anineteenth example is an acoustic wave device as described in the firstexample, in which the resonant frequency of the acoustic wave device isin UNII-3 band 9042, as shown in FIG. 9A. A twentieth example is anacoustic wave device as described in the first example, in which theresonant frequency of the acoustic wave device is in UNII-4 band 9043,as shown in FIG. 9A. A twenty first example is an acoustic wave deviceas described in the first example, in which the resonant frequency ofthe acoustic wave device is in UNII-5 band 9044, as shown in FIG. 9A. Atwenty second example is an acoustic wave device as described in thefirst example, in which the resonant frequency of the acoustic wavedevice is in UNII-6 band 9045, as shown in FIG. 9A. A twenty thirdexample is an acoustic wave device as described in the first example, inwhich the resonant frequency of the acoustic wave device is in UNII-7band 9046, as shown in FIG. 9A. A twenty fourth example is an acousticwave device as described in the first example, in which the resonantfrequency of the acoustic wave device is in UNII-8 band 9047, as shownin FIG. 9A.

FIG. 10 illustrates a computing system implemented with integratedcircuit structures or devices formed using the techniques disclosedherein, in accordance with an embodiment of the present disclosure. Ascan be seen, the computing system 1000 houses a motherboard 1002. Themotherboard 1002 may include a number of components, including, but notlimited to, a processor 1004 and at least one communication chip 1006A,1006B each of which may be physically and electrically coupled to themotherboard 1002, or otherwise integrated therein. As will beappreciated, the motherboard 1002 may be, for example, any printedcircuit board, whether a main board, a daughterboard mounted on a mainboard, or the only board of system 1000, etc.

Depending on its applications, computing system 1000 may include one ormore other components that may or may not be physically and electricallycoupled to the motherboard 1002. These other components may include, butare not limited to, volatile memory (e.g., DRAM), non-volatile memory(e.g., ROM), a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth). Any of the components included in computingsystem 1000 may include one or more integrated circuit structures ordevices formed using the disclosed techniques in accordance with anexample embodiment. In some embodiments, multiple functions may beintegrated into one or more chips (e.g., for instance, note that thecommunication chips 1006A, 1006B may be part of or otherwise integratedinto the processor 1004).

The communication chips 1006A, 1006B enables wireless communications forthe transfer of data to and from the computing system 1000. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chips 1006A, 1006B mayimplement any of a number of wireless standards or protocols, including,but not limited to, Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+,HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivativesthereof, as well as any other wireless protocols that are designated as3G, 4G, 5G, and beyond. The computing system 1000 may include aplurality of communication chips 1006A, 1006B. For instance, a firstcommunication chip 1006A may be dedicated to shorter range wirelesscommunications such as Wi-Fi and Bluetooth and a second communicationchip 1006A may be dedicated to longer range wireless communications suchas GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, 5G and others. In someembodiments, communication chips 1006A, 1006B may include one or moretemperature compensating acoustic wave devices 1008A, 1008B (e.g.,resonators, e.g., filters, e.g., oscillators) as variously describedherein (e.g., temperature compensating acoustic wave devices including astack of alternating axis piezoelectric material). Temperaturecompensating acoustic wave devices may be included in various ways,e.g., one ore more resonators, e.g., one or more filters, and e.g., oneor more oscillators. Further, such temperature compensating acousticwave devices 1008A, 1008B, e.g., resonators, e.g., filters, e.g.,oscillators may be configured to be Super High Frequency (SHF)temperature compensating acoustic wave devices 1008A, 1008B or ExtremelyHigh Frequency (EHF) temperature compensating acoustic wave devices1008A, 1008B, e.g., resonators, e.g., filters, e.g., oscillators (e.g.,operating at greater than 3, 4, 5, 6, 7, or 8 GHz, e.g., operating atgreater than 23, 24, 25, 26, 27, 28, 29, or 30 GHz, e.g., operating atgreater than 36, 37, 38, 39, or 40 GHz). Further still, such Super HighFrequency (SHF) temperature compensating acoustic wave devices orExtremely High Frequency (EHF) resonators, filters, and/or oscillatorsmay be included in the RF front end of computing system 1000 and theymay be used for 5G wireless standards or protocols, for example.

The processor 1004 of the computing system 1000 includes an integratedcircuit die packaged within the processor 1004. In some embodiments, theintegrated circuit die of the processor includes onboard circuitry thatis implemented with one or more integrated circuit structures or devicesformed using the disclosed techniques, as variously described herein.The term “processor” may refer to any device or portion of a device thatprocesses, for instance, electronic data from registers and/or memory totransform that electronic data into other electronic data that may bestored in registers and/or memory.

The communication chips 1006A, 1006B also may include an integratedcircuit die packaged within the communication chips 1006A, 1006B. Inaccordance with some such example embodiments, the integrated circuitdie of the communication chip includes one or more integrated circuitstructures or devices formed using the disclosed techniques as variouslydescribed herein. As will be appreciated in light of this disclosure,note that multi-standard wireless capability may be integrated directlyinto the processor 1004 (e.g., where functionality of any chips 1006 isintegrated into processor 1004, rather than having separatecommunication chips). Further note that processor 1004 may be a chip sethaving such wireless capability. In short, any number of processor 1004and/or communication chips 1006 may be used. Likewise, any one chip orchip set may have multiple functions integrated therein.

In various implementations, the computing device 1000 may be a laptop, anetbook, a notebook, a smartphone, a tablet, a personal digitalassistant (PDA), an ultra-mobile PC, a mobile phone, a desktop computer,a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player, adigital video recorder, or any other electronic device that processesdata or employs one or more integrated circuit structures or devicesformed using the disclosed techniques, as variously described herein.

Further Example Embodiments

The following examples pertain to further embodiments, from whichnumerous permutations and configurations will be apparent. The foregoingdescription of example embodiments has been presented for the purposesof illustration and description. It is not intended to be exhaustive orto limit the present disclosure to the precise forms disclosed. Manymodifications and variations are possible in light of this disclosure.It is intended that the scope of the present disclosure be limited notby this detailed description, but rather by the claims appended hereto.Future filed applications claiming priority to this application mayclaim the disclosed subject matter in a different manner, and maygenerally include any set of one or more limitations as variouslydisclosed or otherwise demonstrated herein.

1. A bulk acoustic wave resonator comprising: a substrate; and a piezoelectric stack comprising first and second piezoelectric layers acoustically coupled with one another to have a piezoelectrically excitable resonance mode, in which the first piezoelectric layer has a first piezoelectric axis orientation, and the second piezoelectric layer has a second piezoelectric axis orientation that substantially opposes the first piezoelectric axis orientation of the first piezoelectric layer, and in which the first and second piezoelectric layers have respective thicknesses so that the bulk acoustic wave resonator has a main resonant frequency that is in one of a super high frequency band and an extremely high frequency band, in which the first piezoelectric layer includes a first pair of piezoelectric sublayers, and a first temperature compensating layer.
 2. The bulk acoustic wave resonator as in claim 1 comprising an acoustic reflector electrode including a first pair of metal electrode layers electrically and acoustically coupled with the first and second piezoelectric layers to excite the piezoelectrically excitable resonance mode at the main resonant frequency of the bulk acoustic wave resonator.
 3. The bulk acoustic wave resonator as in claim 2 in which: the acoustic reflector electrode is a top acoustic reflector electrode; and the first pair of metal electrode layers is a first pair of top metal electrode layers.
 4. The bulk acoustic wave resonator as in claim 2 in which: the acoustic reflector electrode is a bottom acoustic reflector electrode; and the first pair of metal electrode layers is a first pair of bottom metal electrode layers.
 5. The bulk acoustic wave resonator as in claim 3 comprising a bottom acoustic reflector electrode including a first pair of bottom metal electrode layers.
 6. The bulk acoustic wave resonator as in claim 5 in which a first mesa structure comprises the piezoelectric stack, and a second mesa structure comprises the bottom acoustic reflector electrode, and a third mesa structure comprises the top acoustic reflector electrode.
 7. The bulk acoustic wave resonator as in claim 1 in which the first temperature compensating layer is interposed between first and second members of the first pair of piezoelectric sublayers.
 8. (canceled)
 9. The bulk acoustic wave resonator as in claim 1 in which the piezoelectric stack comprises a second temperature compensating layer, in addition to the first temperature compensating layer.
 10. The bulk acoustic wave resonator as in claim 1 in which the second piezoelectric layer comprises: a second pair of piezoelectric sublayers having the second piezoelectric axis orientation; and a second temperature compensating layer interposed between first and second members of the second pair of piezoelectric sublayers.
 11. The bulk acoustic wave resonator as in claim 3 in which: the top acoustic reflector electrode comprises a connection portion of the top acoustic reflector electrode; and a gap is formed beneath the connection portion of the top acoustic reflector electrode adjacent to an etched edge region extending through the first piezoelectric layer; and the gap is filled with at least one of air and a dielectric material.
 12. The bulk acoustic wave resonator as in claim 2 in which members of the first pair of metal electrode layers of the acoustic reflector electrode are different metals from one another having respective acoustic impedances that are different from one another so as to provide an acoustic impedance mismatch at the main resonant frequency.
 13. (canceled)
 14. The bulk acoustic wave resonator as in claim 2 in which: the acoustic reflector electrode includes a second pair of metal electrode layers electrically and acoustically coupled with the first and second piezoelectric layers to excite the piezoelectrically excitable resonance mode at the main resonant frequency; and members of the first and second pairs of metal electrode layers have respective acoustic impedances in an alternating arrangement to provide a plurality of acoustic impedance mismatches.
 15. The bulk acoustic wave resonator as in claim 10 comprising a third piezoelectric layer, in which the first, second, and third piezoelectric layers have respective piezoelectric axis orientations that substantially oppose one another in an alternating arrangement.
 16. (canceled)
 17. The bulk acoustic wave resonator as in claim 1 comprising a second pair of piezoelectric layers and further comprising at least one or more of: a third pair of piezoelectric layers, a fourth pair of piezoelectric layers, a fifth pair of piezoelectric layers, a sixth pair of piezoelectric layers, a seventh pair of piezoelectric layers, an eighth pair of piezoelectric layers and a ninth pair of piezoelectric layers, in which the pairs of piezoelectric layers have alternating piezoelectric axis orientations.
 18. The bulk acoustic wave resonator as in claim 1 in which the main resonant frequency of the bulk acoustic wave resonator is in a 3rd Generation Partnership Project (3GPP) band.
 19. The bulk acoustic wave resonator as in claim 1 in which the main resonant frequency of the bulk acoustic wave resonator is in at least one of a 3GPP n257 band, a 3GPP n258 band, a 3GPP n260 band, and a 3GPP n261 band. 20-28. (canceled)
 29. The bulk acoustic wave resonator as in claim 1 in which the main resonant frequency of the bulk acoustic wave resonator is in an Institute of Electrical and Electronic Engineers (IEEE) band in one of a Ku band, a K band, a Ka band, a V band, and a W band.
 30. The bulk acoustic wave resonator as in claim 1 in which the main resonant frequency of the bulk acoustic wave resonator is in an Institute of Electrical and Electronic Engineers (IEEE) band in one of a Ku band, a K band, a Ka band, a V band, and a W band, and in which the bulk acoustic wave resonator has a quality factor of approximately 730 or greater at the main resonant frequency of the bulk acoustic wave resonator. 31-32. (canceled)
 33. The bulk acoustic wave resonator as in claim 1 in which the main resonant frequency of the bulk acoustic wave resonator is in a millimeter wave frequency band. 34-36. (canceled)
 37. The bulk acoustic wave resonator as in claim 1 in which the main resonant frequency of the bulk acoustic wave resonator is in an Unlicensed National Information Infrastructure (UNII) band.
 38. (canceled)
 47. An electrical filter, comprising a plurality of bulk acoustic wave resonators over a substrate, in which at least one of the plurality of bulk acoustic wave resonators comprises a piezoelectric stack comprising first and second piezoelectric layers having a piezoelectrically excitable resonance mode and a main resonant frequency, in which the first piezoelectric layer comprises a first pair of piezoelectric sublayers, and a first temperature compensating layer.
 48. The electrical filter as in claim 47, in which the at least one of the plurality of bulk acoustic wave resonators comprises an acoustic reflector electrode including a first pair of metal electrode layers electrically and acoustically coupled with the first and second piezoelectric layers to excite the piezoelectrically excitable resonance mode at the main resonant frequency.
 49. The electrical filter as in claim 47 in which: the at least one of the plurality of bulk acoustic wave resonators comprises at least one additional piezoelectric layer; the first piezoelectric layer has a first piezoelectric axis orientation; and the at least one additional piezoelectric layer has a piezoelectric axis orientation that substantially opposes the first piezoelectric axis orientation.
 50. An electrical oscillator, comprising: electrical oscillator circuitry; and a bulk acoustic wave resonator coupled with the electrical oscillator circuitry to excite electrical oscillation in the bulk acoustic wave resonator, in which the bulk acoustic wave resonator includes a piezoelectric stack comprising first and second piezoelectric layers having a piezoelectrically excitable resonance mode, and in which the first piezoelectric layer includes a first pair of piezoelectric sublayers, and a first temperature compensating layer.
 51. The electrical oscillator as in claim 50 in which the piezoelectric stack comprises a second temperature compensating layer.
 52. The electrical oscillator as in claim 50 in which: the first piezoelectric layer has a first piezoelectric axis orientation; and the second piezoelectric layer has a second piezoelectric axis orientation that substantially opposes the first piezoelectric axis orientation of the first piezoelectric layer.
 53. The electrical oscillator as in claim 51 in which the bulk acoustic wave resonator includes an acoustic reflector electrode including first and second pairs of metal electrode layers electrically and acoustically coupled with the first and second piezoelectric layers.
 54. An acoustic wave device comprising: a substrate; a piezoelectric stack comprising a first piezoelectric layer having a first piezoelectric axis orientation, in which the first piezoelectric layer includes a first pair of piezoelectric sublayers, and a first temperature compensating layer; and the piezoelectric stack further comprising a second piezoelectric layer acoustically coupled to the first piezoelectric layer, the second piezoelectric layer having a second piezoelectric axis orientation that is antiparallel to the first piezoelectric axis orientation.
 55. The acoustic wave device of claim 54, comprising a first metal acoustic wave reflector electrode electrically interfacing with the first piezoelectric layer, the first metal acoustic wave reflector electrode comprising first and second pairs of metal electrode layers.
 56. The acoustic wave device of claim 55, comprising a second metal acoustic wave reflector electrode electrically interfacing with the second piezoelectric layer, the second metal acoustic wave reflector electrode comprising third and fourth pairs of metal electrode layers.
 57. The acoustic wave device of claim 54, comprising a third piezoelectric layer disposed between the first piezoelectric layer and the second piezoelectric layer and being acoustically coupled to the first piezoelectric layer and the second piezoelectric layer.
 58. The acoustic wave device of claim 57, comprising a fourth piezoelectric layer disposed between the first piezoelectric layer and the second piezoelectric layer and being acoustically coupled to the first piezoelectric layer and the second piezoelectric layer and the third piezoelectric layer, in which the piezoelectric stack further comprises a second temperature compensating layer.
 59. An acoustic wave device, comprising: a piezoelectric stack comprising a first temperature compensating layer and a plurality of piezoelectric layers having alternating parallel and antiparallel piezoelectric axis orientations, the plurality of piezoelectric layers having respective thicknesses, the respective thicknesses facilitating a main acoustic resonance frequency of the acoustic wave device; and a first metal acoustic wave reflector electrode comprising a first plurality of pairs of metal electrode layers electrically interfacing with a first piezoelectric layer of the plurality of piezoelectric layers, in which the first layer of piezoelectric material includes a first pair of piezoelectric sublayers, and the first temperature compensating layer.
 60. The acoustic wave device of claim 59 comprising a second metal acoustic wave reflector electrode comprising a second plurality of pairs of metal electrode layers electrically interfacing with a second piezoelectric layer of the plurality of piezoelectric layers. 61-63. (canceled) 